We happen to be debating this one right now. A little history is in order--when I had #3, my older two were DD7 and DS6. We decided they wouldn't be present--too young, etc. Well, DD, in particular, devoted hours to preparing for the birth--reading birth books and our EMT books, etc.--she knew about episiotomies and the cephalic position, etc. The first two I was induced, so arranging childcare as needed was no problem--with #3 we had a neighbor lined up, but had no idea if I would be early or late, how long labor would be, etc. It turns out, we got to the hospital at 8:35 pm and had DD2 at 9:12 pm--even the doctor missed it! I had 5-6 of the really nasty contractions, and she was out--delivered by 3 nurses and her dad, 9 days early. DD#1 was miffed that she missed it.
Now, I'm pregnant with #4 (and the last of the line), due 3/5. We live 40 minutes from the hospital on a good day, and since 3/3 were early, I have visions of birthing in front of the wood stove during a blizzard (did I mention we live inthe Adirondacks?). So, we are prepping DD10, as a "plan C". Believe me, she's not our first choice, but given the circumstances, and her interest, I feel it's safer to plan than not! (BTW plan A is the hospital, plan B is DH). We've also promised her that, this time, she can go to the hospital if I don't have to pull her out of school (considering our timing last time, i don't want to risk the time). DS8 is a completely different story--he's more sensitive and may have issues. As the time draws closer, we'll do our best to prepare him for any scenario, but I think being in the delivery room would scare the snot out of him. And adorable as DD2 is, she would be more of a hinderance than any kind of help, and we won't need the distraction.
So, that's my answer. In a perfect world, I would just take the oldest, but she's shown her maturity in many ways that make me give that answer.
As far as people inviting their whole family (parents, aunts, etc.) in there--well, who am I to argue if you want it that way, but I think my dad would have rather had root canal, and so would my brothers!