If it's in joint tenancy he'll own 100% when she dies, but maybe that's what you meant.  There are rules about gifts of mortgaged property, but I might be thinking of charitable contributions. In any case, these are questions that should have been asked before they acted.  I always tell parents who consider hillbilly probate like this, to hope they don't end up with IRS as a creditor and a former daughter-in-law as a partner.