They also need a degree or a minor in the fraud known as "Family Law" which has no place in our legal system.
Why acknowledge those people? They’re NPCs. Pretend they don’t exist, because in the world of making things happen, they don’t.
As far as ‘Family Law’, to rules to live by:
1) Choose very damn wisely who you shack up with.
2) Keep separate money always. It cuts way down on arguments between you about money and it makes it crystal clear who owns what. You’d be amazed how much harder it is to claim something’s yours when you didn’t pay for it. When in doubt about your partner’s ability to be reasonable about such things, see rule number one.