Hi, K.!
It's a no brainer to me, because I would just have both the girls in bed with me! : )
But, it's easy for me to say that, because I believe in co-sleeping and think the CIO idea is barbaric. : )
My 10 yo boy and 7 yo girl no longer sleep with me (unless they come in after a nightmare) but they did when they were young. My son slept with me until he was two, and my daughter until she was 18 months. I honestly cannot remember how I transitioned them into their own beds. It was just a very natural thing. I think they were getting too crowded, and wanted their own space.
I know you asked us moms for our opinions, but I hate for you to listen to someone say co-sleeping is dangerous and bad. It's not. (Unless you drink a lot or use drugs. Then it's not safe, of course.) And there are no statistics to back up the claim that more SIDS cases are co-sleepers. And the children WILL eventually get into their own beds. Anyone who has a 9 or 10 yo still needing to sleep with them obviously has some other issues going on.
And on the other hand, I don't think you should listen to anyone's ideas that letting your children CIO are going to permanently damage them, pyschologically or otherwise. There are millions of children who have been through it, and survived. Heck, I'm sure WE went through it, too, and we're okay, aren't we? ; )
Ultimately, you have to do what is best for your family, and only you can know that. Just trust your instinct, and if it doesn't feel right, it's not! Whatever you end up choosing to do, all of you will eventually adjust, and your girls will be just fine.
Blessings, J.