My guess is that the younger couple doesn't have enough financial information to begin to make any transition decisions. With accurate accounting, they will have, at least, a clean shot at sharing benefit and risk equitably among them as business partners. Even if they decide to dissolve the partnership, accurate accounting will be essential to accomplish that without litigation. Partnerships can work, even between people who don't especially like each other. But workable partnerships are based on clear agreements and a balancing of risk and benefit.
Accurate numbers are the foundation for both.
S.J. shouldn't hesitate to begin the process. Although Jim and Mary may resist at first, S.J. probably will find they are just as eager as she is to put everything on a factual footing. In reality, years of silent but festering dissension aren't easily erased. The odds are about equal that it's already too late, and they'll need a clean break. But they have no chance at all if they fail to put their partnership on a sound, businesslike footing.