If you buy seat reservations and miss the train with your reserved seats (or take an earlier train), your reservations will be void (no refund) but do not affect your ticket.

When you arrive with the 3:00pm flight from SFO on UA, you'll arrive in Terminal 1 and when you just follow the signs to "Fernbahnhof" (Long distance trains; there is also a second train station for regional trains only, make sure you walk to the one for long distance trains) then you will be at the train station probably no later than 3:45-4:00pm. Immigration and customs won't take that long. Therefore, I do not recommend the saver tickets 1st class at 5:20pm.

I'd recommend to buy regular tickets only (122.00€).
However: Please make sure that you choose "2 adults + 2 children 6-14". They are free, but only when they are printed on the adults ticket! If that's not the case, then they will have to pay the full (!) fare on the train (+10%). (http://www.bahn.com/i/view/USA/en/pr...ard_fare.shtml).

And: Seat reservations are only usefull if you have them for everyone (i.e. 4 reservations).
I'd recommend seat reservations as you are a party of four. Even though at that time during the week, the trains will not be very crowded, but you might have a hassle finding four seats next to each other.

When you go to http://www.bahn.de/i/view/USA/en/ to book and change the "Passengers" to "2 adults" and "2 children 6-14" then the system will automatically recommend to reserve 4 seats (4.00€ each = 16.00€).


I'd reserve the 4:53pm but you might even catch the 3:53pm train (where you have to change trains in Mannheim, but that is very simple: the connecting train will wait on the opposite side at the same platform (so it's only: leave the train, walk 30 feet, enter the connecting train).



Enjoy Germany and enjoy your new German car.