Confused about train tickets

The problem is that you are looking to travel on a Saturday. Due to weekend engineering work the booking window can be a lot shorter than 12 weeks anywhere in the UK. I have checked and neither South Western Railway or LNER are currently open for bookings for that date, The cheapest route would always be split ticketing- Salisbury to London Waterloo, and London Kings Cross to York, leaving a minimum 90 minutes for transfer across London, although it takes less than 30 minutes for the transfer by tube IF the first train is on time and IF the tubes haven't got engineering closures. You can avoid London by using Cross Country Trains but that will always be more expensive. When booking opens you should get it for about £65 (maybe cheaper- I can see it on other weeks for just over £40) . All you can do is sign up for alerts on both SWR and LNER websites, LNER is likely to open first but don't book either leg until both sectors are open, in case there is a line closure on either leg. Some Saturdays in March there are no trains out of Kings Cross at all (instead you have to go to Bedford, then a bus back across to LNER at Peterborough)- those weeks no cheap fare is available. On those weeks the cheapest fare would be complex split ticketing from St Pancras to Sheffield and Leeds. Anyone currently offering cheap tickets (or any tickets) is not being honest ("too good to be true"), as in time the trains may not exist. At very worst it could only be a week or two before hand when bookings open but that would be unusual. Transport for London put an e-mail out every Thursday for that weekend's engineering work. When bookings open both legs can be booked on the LNER website.

Thank you so much for that detailed explanation. That is exactly what I was thinking but just needed confirmation as I don't fully understand all the logistics.

I've signed up for alerts from LNER. Will also for SWR.

Thank you again!

For LHR to Salisbury, the easiest way is to take the RailAir coach from Heathrow to Guildford (get off at Woking).

You want the RA2 service – the website is a bit rubbish https://www.firstbus.co.uk/railair/buy-tickets

Then train from Woking to Salisbury – Advance tickets from £5 – a walk-up buy at the station ticket £25.

Are you writting in American or British? 5 April or 4 May?

By the way you can't buy a railcard at LHR (there seems to be much debate on that as Heathrow Express and Elizabeth Line are both National Rail- but that is the consensus of opinion), that would need to be purchased at Woking. It doesn't matter as it's not valid on the rail link coach. Or buy it beforehand as a digital railcard. I don't know about Two Together but a Senior Railcard gives you 1/3 off London tube fares as well- you have to register it with staff at an LUL station.

I was just at the Elizabeth Line and Heathrow Express platforms and stations at T4, T2/3, T5 at Heathrow.

There is NO booking office or ticket booth there. There are 2 or 3 machines at each station, just 1 or 2 at T4. Nothing more. Nobody to sell you a Railcard. Really.

I've caught a little flak in other discussions for having questions about the train and coach systems. It's discussions like this one that make this newbie feel better about trying to nail down all the details in advance.

@Charlie--your train post and this one are the ones that caused me to post my question about the ability to buy railcards at LHR. I'm glad to see word is getting around that it's not possible. Should be fewer surprised/unhappy travelers that way.

Thank you for all of the information and kind help. It's very confusing for Americans to navigate who don't have any rail system at all.
To clarify, I am writing in American dates. The dates are April 5 and April 8.
For the April 5, I will look into the coach.

After reading all of the comments (thank you for this so there weren't surprises), I'll buy the 2 together pass online.

I'm still concerned about the rail tickets for April 8 where we'll be going from Salisbury to York. Will someone please put an eye to what I'm seeing and tell me if it is okay to purchase (and if I'm understanding everything properly). I found it to be less expensive to buy tickets from Salisbury to Kings Cross, then another from Kings Cross to York (rather than just a direct).

I looked at South Western Railway on April 8 from Salisbury to London Kings Cross. It is giving me a price of 66 pounds but has the disclaimer
"We don't yet know if this journey will be affected by engineering work. Please check back closer to the time of travel."
Does this mean I could potentially buys both segments, SAL to KGX then another KGX to YRK and run the risk of the SAL to KGX being cancelled?

I can wait longer as suggested above but I'm also trying to keep the fares lower which everything I've read says to purchase well in advance.

Again, thank you all so very much for all of the great help with this.

Firstly you want to buy Salisbury to Waterloo and then King’s Cross to York and separately take the tube between the two.
Secondly, whilst weekend travel is always a bit more complex than weekday April 8th is particularly difficult as it’s Easter weekend. This is one of the times when more major engineering work is undertaken so the chance of such work affecting your journey is that much greater..

If you go on the LNER website you can see tickets from London to York on 8 April for £31. There’s a caveat that the timetable hasn’t been confirmed yet, but no engineering work is scheduled so if there are any changes I expect they would be minor. So you can book that leg now.

The problem is the Salisbury to London route where there is engineering work on 8 April. The timetable could be significantly altered. There might even be replacement bus services for part of the route. On any other Saturday, you can get cheap tickets for £9 (see April 1st). But until the timetable is confirmed you just have to wait.

What you could do (as bookings are now open) is book a KX to York ticket for mid afternoon (1530 onwards) as, if all else fails, there is a National Express coach from Salisbury to London Victoria at 0950 which arrives at Victoria at 1320 for £10.10 each (today's fare). The reality is that, if there is planned engineering, then the affected section of route will have a bus replacement. So that allows plenty of time for train-bus-train changes. There will be some kind of service through engineering work, not outright cancellation.
There may be circumstances (if the lines into Waterloo itself were closed for engineering) where you would have to change at Basingstoke, then train Basingstoke to Reading then train Reading to London Paddington. That is why you want to allow lots of time to get into London.
The great unknown is if the rail strikes will still be happening then. If they are then you can be pretty certain that the Easter weekend will be deliberately targeted as a strike day. If that happens (and there has to be 2 weeks warning) then you can continue from London on National Express coach to York at 1630 at 2150. If you booked that coach today it would cost £28 each Salisbury to York.
South Western Railway only operate to Waterloo, not King's Cross. You have to take the tube (or bus) between the two terminals. It is cheaper to purchase Salisbury to Waterloo and the tube fares separately.
Likewise if there is a rail strike on 5 April then there are lots of coaches from Heathrow to Southampton direct with an hourly local bus from Southampton to Salisbury.

Train travel is a mess in the UK. It is now a game of "let's try and get the unaware (also called "the tourists") to pay way more than they should, and give a 'break' to those that are in the know".

Dealing with the rail company you plan to use, yields the cheapest tickets, as does booking as far ahead as they let you - 90 days I think. The difference is sometimes huge - I saw differences of 10 times or more, cheaper.

Thank you all so very much for your fantastic input. It has helped me greatly. I've decided I'll buy the rail tickets (the Kings Cross to York later in the afternoon as suggested) then we'll take our chances on the Salisbury to Waterloo. If there is engineering changes, we'll just go with the flow. And as was also suggested, if there is a strike, I'll have National to fall back on.

I tried to change our travel day away from Saturday but I already have locked in hotel reservations and it would ultimately shorten our time in either Salisbury or York and I don't really want to do that. So, I'll just book it and see what happens, Ultimately, we're on vacation in beautiful country so if we have a little hiccup, it'll be good memories afterwards.

Again, I can't begin to say enough to everyone who has given such valuable and kind information. It has greatly helped me navigate the train system which is very foreign to me as we don't have rails (or really any transportation system other than flying or driving).