Dum se casta vixerit ! We used to have a condition in divorce, and I think in some trusts, called that; it means "for as long as she is chaste"; the effect of which was that the woman's rights ended if she married or cohabited. We don't see it now, the law having moved on (and stopped talking in Latin !), though it is possible that a woman who marries again will not be get maintenance from her ex.
There must be case law on this for the circumstances you describe, which Barmaid will know. The house is now the daughters'. The principal condition is that the friend, of either sex, has the right to live there for life . The non-cohabitation part strikes me as contrary to the friend's human rights and against public policy nowadays. Be interesting to hear from BM for definitive answer.