Eurail seating of 2nd vs 1st class

Even if they have a 1st class pass, your parents would be welcome to sit with you in 2nd class. Alternatively, spend the extra money for a 1st class Saver pass and sit in 1st class with them. You should also carefully consider your planned days of travel and whether a pass would be justified or not. A lot of trains in Europe now require a supplementary fee in addition to the pass. Point-to-point tickets (online from the rail companies or at the counter over there) can often be less expensive.

As Lee says, before buying a pass (any kind), post your itinerary here, and people here can advise if a pass is worth buying in the first place. These days, it's usually cheaper to buy point-to-point tickets in advance, although you do lose flexibility this way. But, as Lee also says, passes aren't as flexible as they once were, because in some countries on some routes, you need to buy a reservation on top of your pass, so you can't just hop on any train at a whim. Furthermore, while reservations in Italy are not restricted, in France they limit the number of seats available to pass-holders, so even if there are empty seats on your train, you may not be able to use your pass, and will have to buy a separate ticket, if you haven't planned ahead. Someone here called this the "dark underbelly" of passes. On the other hand, for some places (Switzerland is a good example), a single country pass (not a Eurail pass) can be a good deal.

As well, in Germany only a few trains (ICE Sprinters) require reservations. For all other express trains, you can always get seat reservations, if you want them, from a station's ticket counter for 4 €. OTOH, German Rail sells advance purchase tickets online starting at a price rail passes can't touch. There are also regional passes (like the Bayern-Ticket) that will give you big savings vs rail passes.

Thank you both very much! My father is set on having even that little bit of flexibility offered by Eurail, so looks like we'll be buying that pass.