I educated my partner about birth and showed him birth videos. We're already "against the grain" as it is, and we believe in doing things as naturally as possible. Natural home birth made sense to both of us, and unassisted was what I wanted, and he wanted whatever I wanted, since I am the one giving birth! He knows how well I know my body and he has watched me birth a few times now...and he's convinced I've made good birth decisions. If my husband didn't support me 100% I'm not sure if I could UC with him around, but I'd probably still birth unassisted because I just know it's right for me.
I'd just tell my kids I'm having a baby. It's a special thing, but not a big deal. If they're awake when I'm in labor and wondering what's up, they'll be told that the baby is coming! Simple as that. I don't think it's a good idea to make it into a big thing where you have to "prepare" them beforehand, but that's my two cents. I am all for treating birth like a normal, everyday event, though a special one!
If I have a longer labor this time (with my history, not likely), I'll invite my best friend over to help watch my kids.
Here's a good online resource that really helped prepare me for birth (not only with good info, but also it mentally/emotionally prepared me). I don't necessarily agree with everything on that website, but, like anything, take it with a grain of salt. The writer (a childbirth educator) has some really excellent points and ideas, as well as good resources.