large fam's and guardians

So we have 3 kids and my wife REALLY wants to be PG again (AF is still on vacation). My question is this, we have a couple that has agreed to take guardianship of our children if something were to happen to my wife or myself. The problem is that their kids are almost grown and out of the house, I suspect they are not going to want to be responsible for many more of our kids (My wife is thinking 6 might be nice but she also is not sure she wants to limit our family to that number either). Most of our friends are not in a position to take a large number of kids and we would not like to see them split up. Neither one of us is keen on the others parents taking over (besides I'm not sure they are keen on our "breeding" plans :lol: ), how have all of you addressed this issue or is it that big of an issue outside of the states?

Good question. I only have two, but with small urban houses and the cost of living being so high, I wonder if how our nominated guardians would take care of our girls, especially if we have 3 or 4 which is what I want.