"The husband is wondering how long can he legally stay in the 'family home' before he has to sell it to pay off his wife. "
There is no time limit. Until one or other of them decides to deal with the separation - which could be weeks or years, he can stay there. Mind you that is not necessarily a good thing - inaction does not fix problems.
"He heard that he can stay there until the daughter turns 22 once she stays in full time education and I'm wondering if anybody else knows if this is true or not?"
Not necessarily. It is persuasive but marital breakdown is so common now that that argument really does not hold water any more. A court is more likely to say, sell house, split proceeds, get on with it.
The parties should talk, agree on what is to happen and implement it. Mediation is a good start.
mf