Five train trips in 10 days

You may be able to find a rail pass that fits your travel or it may be cheaper to buy point to point tickets,
Both options are available
for you to review on the DB rail site

https://www.bahn.com/en/view/offers/passes/index.shtml?dbkanal_007=L04_S02_D002_KIN0060_NAVIGATION-LINKS-PAESSE_LZ01

Also here is a link to a primer on train travel in Germany
https://www.seat61.com/Germany-trains.htm

I don't think that a train pass is worth it since you have just 2 legs to cover with long distance trains.

Frankfurt - Rothenburg: Look for a (train specific) Sparpreis ticket (prices start at € 19.90; book soon at www.bahn.com)
Berlin - Hamburg: dto., prices start at €24.90
Rothenburg - Füssen and Oberstaufen - Munich: travel on a Bayern ticket (€25/1, €31/2, valid after 9am)
Füssen - Oberstaufen If travelling solo buy a regular ticket (€22), for two travellers take a Bayern ticket again.

Are you flying from Munich to Hamburg?

Thank you for the swift replies! Yes..will fly from Munich to Berlin.

My son may have his College ID by the time we travel...so he plans on getting the International Student ID card. Will the savings for traveling as a student be substantial? Or should we just book now for travel in July?

Regrettably, there is no reduction for students at all; everybody over 15yo is considered an adult. Book at least the tickets from Hamburg to Berlin early, because that's a popular connection and the cheapest tickets will disappear soon. OTOH, if discounted tickets are sold out for the Frankfurt - Rothenburg leg, you can still resort to a combination of regional tickets: Frankfurt - Kahl with RMV Ticket (Frankfurt transportation authority), Kahl - Rothenburg with Bayernticket.

The full regional fare for Füssen to Oberstaufen is 26,70€/P.

For Füssen to Oberstaufen, there is a Regio-Ticket Allgäu-Schwaben at 22€ for one, 28€ for two. The Bayern-ticket is 3€ more (for 1 or 2), but would also cover any bus transport in Füssen to get to the Bhf; the Allgäu-Schwaben ticket covers only the train.

For FRA to Rothenburg ob der Tauber using an RMV ticket and a Bayern-Ticket, you need to get from the close-in Regionalbhf at the airport to Frankfurt Hbf, either by regional train or by S-Bahn, then take one of the hourly Regional Expresses (RE) from Frankfurt Hbf to Würzburg. The RMV ticket will cover you from FRA to Frankfurt Hbf plus on the RE to Kahl am Main, the first station in Bavaria, at which time you can start using the Bayern-Ticket (no need to get off the train, just change tickets).

So do I have this right...
Frankfurt to Rothenburg ob der Tauber - buy a one way ticket

Rothenburg - Fussen / Fussen - Oberstaufen / Oberstaufen - Munich .....buy 3 Bayern tickets, each specifically for the days I want to travel, but not for a specific time

Berlin - Hamburg - buy a one way ticket.

For the Bayern ticket....do I have to select the time of travel in advance?

Can I use a Niedersachsen-Ticket for the Berlin - Hamburg ticket? It is 26 euros for 2 tickets, vs 59.80 euros for two one way tickets from Berlin to Hamburg.

You do need to specify a date of travel for a Bayern Ticket, but the normal way to buy them is to go to one of the vending machines in the station right before you travel. Then write the travelers names on the back of the ticket (in ink).

You can't use a Niedersachsen Ticket to go from Berlin to Hamburg because Berlin is in Brandenburg. Technically, both cities are independent of their surrounding Land, but their Laender Tickets cover the surrounding Land. You would heed a Quer durchs Land ticket to travel between them on week days, or a Happy Weekend Ticket. Travel on regional trains with at least 1 connection along the way and a 4+ hour travel time. Cost would 52 and 50 EUR for the respective tickets assuming 2 people.

If you book the ICE ticket now, it could be as low as 49.80 EUR for 2 and take 1 3/4 hour. Train specific. Your choice.

Thanks again for everyone's patience and even more details! I checked for the ICE tickets for Berlin - Hamburg and found them for 39,80 Euros for 2 tickets! Now I finally think I can go ahead and book day 1 and day 9 and get on with the rest of the planning.

Last question: I booked the Frankfurt - Rothenburg ticket for 2 passengers...but it did not give me the option to put another persons name on the reservation, so the ticket has one name on it, but booked 2 seats. Is this ok?

Yes. Your name is on it because you bought it. It's your ticket. You can take anyone you want.

German trains it doesn't matter, just the "lead" traveler. Its not an airplane ticket.

The full regional fare for Füssen to Oberstaufen is 26,70€/P.

@Lee: do they really show a different price from the German website at the American one? It shows me €22 all day round. Do we have to compare prices between different versions of the website in the future?