Hi Amy! I am planning on asking my OB at my next appt when they 'like' or 'expect' them to be head down but I don't think there is a hard and fast rule for when they can no longer turn. A friend of mine had her twins at 37.5 weeks and in an u/s a week beforehand, twin 1 was breech and twin 2 head down. She was told she could have a VB if twin 1 turned. Turned out twin 1 DID turn - but so did twin 2 and twin 2 managed to beat her sister to present at the cervix first so she had to have a c-section after all. So anyway, the point of my story is that BOTH her babies turned completely at 37 weeks. And they were both a good size (7lb plus) for twins so they definitely find the space if they want to!

As for the car seat dilemma, this is one I am facing too. I will have 2 convertible car seats so I think my toddler will have to be on the edge since I can't imagine being able to lift her over the anchorage straps on the baby seats. However, depending on how much room there is (I am planning on having a play around when I buy my last seat) I might see if I can just undo her buckles and let her climb out on her own. I don't know if she'll have enough room or if she'll be old enough/responsible enough to do it but it would certainly be preferable to trying to lift a baby out over her seat - especially when the babies get bigger... I suggest you just try out different combos with your DD and see what suits her best. You can always switch them around if it isn't working anyway...