hiya, heva-leva, welcome to the site, I think it's a brilliant idea, as long as the people get on well and the elderly don't get taken advantage of, why not, everyone wins ;D
we have a similar situation on our site, we have an elderly person who doesn't want to give his plot up, so, one of the people on the waiting list is doing it with him, for a cut of the crops, it's working well, at the moment, we have to see at harvest time, but the person doesn't want loads of produce so his helper should get a good harvest ;D