Traveling from Edinburgh to Wales

It’s a long and tedious drive unless you want to spend a few days on the road diverting to some more interesting places such as the Lake District and Chester. Seven people plus luggage would also involve a large rental people carrier or two vehicles.

There are no direct trains - you would have to change at Crewe or Bristol. Some train journeys involve 3 line changes, which you want to avoid. The train will take more than 7 hours door to door.

Flying would probably be your best option with Flybe.

You could take the Train direct to Crewe with a transfer to Chester. Then take train from Chester direct to Cardiff. This is one of the quickest ways. With that big of a group you might find it simpler to take the train. It can be expensive to travel by train unless everyone can take advantage of the discounts available such as companion fares, senior fares, and student fares. Many of these require traveling during certain hours. Sometimes booking ahead and sales can save money. If you do want to see things on the way. Stop over at Chester and take day trips to Liverpool or Conwy. The Lake District can be very busy with day tripper tours in June. Another option is that you could travel by sedan cars in 2 groups according to interests, and just meet at arranged midway location like Chester. Or take the train to Chester and then rent autos for a drive thru Wales on the way down to Cardiff.

Take a look at www.nationalrail.co.uk and put in for a journey from EDB > CDF for say early March (best to avoid Sundays and Mondays & Fridays for cheapest fares). Now, you will see various prices and routes. The longer ones are going via Newcastle. What you want is the shortest route and with only 1 change. I see that a Virgin Train leaves EDB at 10.52 (for London Euston) and arrives Crewe at 13.57 on Platform 5. You then would go to Platform 6 (double check on day) for the 14.09 departure to Cardiff arrive at 16.54. Total journey 6 hours and 2 minutes. The price I am getting is £72.50 - but, we don't want to pay that do we? Now put in for the same departure from EDB but this time only as far as CRE. You should get a price of £21 but maybe even less - depending on day/demand for these cheap advance fares. Then do the same for a CRE > CDF departure at 14.00. You should get a price of £25.50. So, we now have the price down to £46.50 (or thereabouts) using exactly the same trains but ticket splitting. You can reduce that even further by buying a group save ticket - see for Virgin Trains:>https://www.virgintrains.co.uk/tickets/your-ticket/group-travel/

Now, you might also be able to buy the ticket with group save for the Crewe to Cardiff leg even though it is not Virgin Trains - it is Transport for Wales. If Virgin can’t do this with the discount, go to Transport for Wales direct. (In the unlikely event that you miss the Cardiff train at Crewe due to the Virgin being late, you would have to wait an hour for the next train to Cardiff using the direct route).
Retain your Virgin Tickets as proof that you have travelled from Edinburgh and that is why you are not on the booked train due to delay. Therefore, you should not incur a penalty fare from Transport for Wales.

Kathleen has offered sound advice (above). I would also consider that you should go from Edinburgh to Chester (one change required) and stay in Chester for maybe 2 nights or so. You could, from here, take a day trip by train to see Conwy (Conway) Castle in north Wales. However, I should also mention that it is NW Wales that has some fine scenery in the Snowdonia National Park. (Most of Wales is scenic). Anyway, you will find direct trains go from Conwy and Chester to Cardiff. (The line mostly follows the Wales/England border). See map of rail routes:>http://www.nationalrail.co.uk/static/images/structure/css/nationalrailnetworkmap.pdf

Note: that to get the cheap ‘advance fares for specific trains’ , you need to book these about 11 weeks ahead - before they up the prices. (Check the pay on the day fares as well - for short journeys, there is no difference). Also consider :> https://www.railcard.co.uk

This is the airline that flies from Edinburgh to Cardiff:>https://www.flybe.com
https://www.visitcheshire.com/chester
http://www.conwy.com
https://www.visitwales.com

If it was me I would fly, there are 2 flights a day I think, but if you plan on renting a car once you arrive in Cardiff this is much more simply done at the airport than in the city centre. They are cheap flights as well although the flights will already be available for June I believe so get booking early.