I know that this thread is 3 years old, but since it popped up in Google, I figured this information might be helpful to other parents of two children (twins or not).
FYI, we're expecting twins soon and we got two Maxi-Cosi Mico car seats barely used. While researching, I've found that the Baby Jogger City Select double will handle the Mico car seats with their adapters. It's very pricy ($500 as a single, $659 as a double, plus $60 each for the car adapters), but the stroller will be good for up to 5 year old kids. Here are several good youtube videos about the stroller...we're definitely considering this, even with the high price.
Good luck!
[ame="http://www.youtube.com/watch?v=LoUq_sZKi-U&feature=related"]YouTube - Baby Jogger City Select Tandem Video Demo from twins-store.co.uk[/ame]
[ame="http://www.youtube.com/watch?v=fF-XtEAy27k"]YouTube - Baby Jogger City Select Double Stroller Reviews, Features & Demonstrations[/ame]
[ame="http://www.youtube.com/watch?v=sdeMgSm-xe0&feature=fvst"]YouTube - Baby Gizmo Baby Jogger City Select Stroller Review[/ame]