I don't usually get into recommending any particular brand of piano... but I have to say that if you can figure out the maintenance budget challenge in terms of your funders, etc. I, too, would recommend Yamaha.... for the reasons mentioned above, and for one other important reason that has to do with the seniors you mentioned as being an integral part of this pianos's purpose. In my experience playing for a variety of folks, I have noticed that those who are more senior in age seem to really prefer bright pianos (and not perceive them as terribly bright). I suspect this has to do with high frequency hearing loss that happens to us all over time. Yamahas tend to be bright. Not all of them. But many of them. Might be worth considering regardless of whether you go with a real piano OR a digital system of some kind (in which you'd really have to look into the sound reproduction qualities of the speakers, etc. ).
I will add that, as a sometimes-pro player myself, a digital is not attractive to me, but rather a sometimes-necessary compromise. Of course, when a real piano is not maintained, a digital might become the more desirable choice... but that is a case of dealing with the least UNpalatable choice. A well-maintained, quality instrument serves as a delicious invitation to me, personally. I might add, too, that if you can somehow get yourself into a decent grand of some sort, that will serve better to attract and serve musicians of all types. If you do have to go with an upright, though, get a tall studio upright.
As for your funding requirements... at some point a digital piano will break or become obsolete and you will have additional costs down the road regardless. I'm not sure how any funder could expect that you would NOT have any additional costs down the road that you would have to expect and plan for in whatever manner you could reasonably do so. Not that it's wise to question funders too much... but... maybe some additional clarification of some sort might help?
You might also see what networking you can do in terms of getting matching funds from donors, or even just a straight-up donation of an instrument from some local company or private party that carries no restrictions. It's always worth a try asking and sometimes it's surprising what people are willing to give if you state your case well enough (and do so face to face, btw - yes, I've done some fund-raising myself). It doesn't hurt to offer something to them in return, too... something that can be a sort of "win-win"... like a plaque offering them permanent recognition (and publicity), or offering them publicity opportunities by mentioning them in event publicity, etc. (esp. if you had a debut event featuring the instrument). Just a couple thoughts.
I'll be interested in hearing how this goes! Feel free to PM me if you want to talk more about it... I'd be interested in hearing more about your project and where you are... Whatever the case, good luck!!!
JH