Look below:

Ummmm.... wow! That's one I haven't seen!

OMG how'd you do that?

I found that one of my family's moms had died, so I let the dad remarry, but instead of the family tree refreshing, I got stuck with two moms!

Coool

Whooooa! That's cool!

I don't like it when the original parents get replaced on the tree I'd be sad!

I guess I haven't run into that issue because I've never had a couple that didn't have a child right after they get married.

When you get a proposal, press alt=f4 without rejecting or accepting it. When you get back on, the game will show that the woman (or man) isn't married if you look at the Family Tree. But your peep actually did marry the peep who proposed. And if the person shown on the Tree dies, even if you have all the children you can get, the husband or wife whom isn't shown, can get proposals and accept them.

EDIT: I looked for the thread that told more about this, but I couldn't find it.

That's like when you press the Esc button instead of choosing marry or reject and your peep just shows up as married anyway. I never checked the family tree though to see if that works the same way as Alt+F4.

I try to avoid bypassing the game's 10 minute save system just in case something really messed up happens

Yes, I know it'll mess the game up. I don't do it, because the result is just too disgusting to me. LOL!