'Spouse' would be a contracted relationship. 'DeFacto' currently, would be a relationship without contract. But you could just say 'parents'. You don't have to link the parents together in a marriage, to have them both be the parents of a profile. On the other hand, www.wikitree.com/wiki/Molesworth-184 William didn't marry Ellen, but I have them connected together, without a marriage date or location. It really isn't an issue.