Rail Travel `

Anything having to do with railroads, ask the Man in Seat 61 who has either rode that way or knows how to do it . www.seat61.com

Germany sure doesn’t make rail passes easy to decipher. But they certainly exist. For Munich, check out this site. There are group day tickets for up to 5 people. Which ticket you need depends on how far you plan to travel. You can use this to get to Dachau. We used it for our group of 4. https://www.mvv-muenchen.de/en/tickets-and-fares/tickets-daytickets/index.html

The DB Navigator app is pretty good about guiding you to passes that work for your group. I’m not familiar with your other destinations to suggest passes for them.

Normally Friedrichshafen to Überlingen would be a train, so it looks like on your travel day this is a bus substitution. But train tickets will be valid.
For your trips in around Münich look at the different MVV offers as already mentioned.
For the trip to überlingen (and back) just book tickets in advance to get a Sparpreis.

For your stay in Überlingen look at the Bodensee ticket.
https://www.bodensee-ticket.com/en/zones/

I spend a month in Überlingen in 1988 to learn German. It is an nice area.

what time does your flight for Cambridge get into Heathrow?

Are your friends right in Cambridge or nearby?

Are you saying that you will be based in Cambridge and taking 3 days of day trips to London? Will you have relaxed breakfasts with your Cambridge friends and then heading off for one major attraction (will your Cambridge friends go into London with you? - will all 4 of you from the flight all go into London each time - will you be spending tourist time in and around Cambridge and vicinity? = so many questions!!) or will you be up like a scalded cat each morning and going into London with the trains full of commuters?

Cambridge is a pretty long way from Heathrow for your flight home. Sure hope that your flight is really late in the afternoon - you will need to allow 3 hours at the airport for your home-bound flight. If planning on going by train (Thameslink to Farringdon and Elizabeth Line or Great Northern (fastest) to Kings Cross than tube or Thameslink to Farringdon to Elizabeth Line) Sundays often attract engineering work and detours.

The pain free way from Cambridge to Heathrow is by direct National Express Bus- takes a little over 2 hours, quite frequent. There are overnight buses for very early flights, and the first daytime buses are at around 5am.
Likewise from LHR there are quiet frequent buses until as late as gone midnight.

That way rail engineering work doesn't affect you.

Yes, you need to sit down and do the math. And you also need to look at what services are offered and what services you want. In particular you should pay attention to the restrictions attached to the cheaper single use tickets. Even the days and times you choose to travel can impact the prices.

For instance in my case I have arthritis in my left leg and the extra space offered by first class is an important comfort for me. But even more important is that if I'm having a bad day and can't move as quick as normal I'm not stuck in having to make a particular connection or I loose my ticket. I can simply hop on a later one.

5) We will then be traveling back to Munich via train to fly out of
Munich at 4:05p the following Wednesday.

If you are staying in Überlingen, why are you backtracking all the way to Munich to fly to London? It would make more sense in my opinion to book a flight from Zürich.