First of all, welcome to MDC!
I know just what you mean about wanting a child of your own. My DSS is 13 and lives with us, but that is only within the last year or so. Before that, he was with his mom most of the time, but we saw him weekly. DH and I have been together for 9 yrs, married for 4. We just had DD 14 months ago, right at the same time DSS came to live with us and it was a pretty challenging adjustment. I think I underestimated how tough it would be and I went a little
for a little bit. :LOL I don't mean to frighten you, but I feel I should be honest. But really, most of my
came from the whole new mom hormones, and just the day to day dealings with a newborn. I'm not sure it would have been much easier if my DSS had not come to live with us at that time. Honestly, he was a HUGE help and loved/loves to play with his baby sister.
Sounds like your DSDs are old enough where they could help out. I think they like that - makes them feel invloved and they get to bond with their new sibling. One of DDs first words was "brother", and he just LOVES that!
Also, made sure to give him a lot of attention on his own, so he wouldn't feel pushed aside by the new baby. That seemed to work well. But I must admit, we sort of slipped up on it for a while recently and he has expressed that he feels left out sometimes. So DH took a few days off work to hang out with him, they've gone to a couple of movies (his fave thing to do) and DSS seems much happier. I think it's something that all families have to keep in check though. It's important that all children, step or bio, feel like they are loved and getting enough good attention, and it's up to the parents to make sure that's happening.
So I guess my point is, yes, it's a big adjustment for everyone. But I think it's totally worth it and I would do it all over again in a heartbeat.