Also what about the adults? What if you find that someone isn't fertile? It's hard enough not being able to conceive when everyone around you seems to be having babies. I can't imagine adding to that the pressure of having to balance out the babies so that everyone has their genetics evenly dispersed. It just seems like a really bad plan. Babies should be brought into the world because THEY are wanted not because it will make the relationship stronger. There are plenty of mono couples who do the same thing to save a relationship. Guess what? It doesn't work. If you have stress or things aren't great as they are having kids just makes that worse!
Everything will be ok in the end. If it's not ok it's not the end.