That is quite an investment you're considering! Money must be some concern (as expected) or why purchase something about 100 years old! I suppose it makes a difference what country you are in as to what may be very available to you. First let me say that I appreciate your interest in enabling your sons to continue developing their skills, but what if they lose interest? I think that unless they are advanced pianists already, you should not aim for the very best, unless of course money is not an issue and you also wish to use the instrument as a status symbol. Otherwise, the important thing is to get good quality. I went VERY far with my Baldwin studio upright, though I did put weights on the keys to make the action heavier. The big leap is the move to a grand piano with its more capable action, wider dynamic range and more resonant bass. I think it is perfectly reasonable to get a "low mileage" smaller grand (sizes around 5'2" or 5'8") that is 10-20 years old if it is of fine quality, which for me would be Baldwin, Steinway or the conservatory (C-x) line from Yamaha. It is important to note that here I mean the top line of grands from these makers, not the intermediate or more economical oriental imports that they sell under other names. There are other options of course. You may wish to consider upgrading the quality and size of the upright (presumed) that they have now. A spinet model is IMO almost not worth owning, but a fine studio or concert upright is an excellent instrument for upto late intermediate and even early advanced playing.
Let us know what you decide in the end.
Eddy M. del Rio, MD
"A smattering will not do. They must know all the keys, major and minor, and they must literally 'know them backwards.'" - Josef Lhevinne