For one baby, I would say skip the infant carrier and go for the convertible seat. We just bought a Diono Radian RXT for our big 2 year old (to replace a Britax Marathon which his baby bro will move into once we ditch the carrier) and we LOVE the Diono. However, with two, the convenience of having both kids contained and being able to easily snap the seat in and out of the base probably supersedes the annoyance of dealing with the carrier seats.
I say probably because it really depends on how much car transport you're planning to do. Do you need to take them on errands a lot? (Some people do that but my husband and I try to plan errands for evenings after bedtime if at all possible, especially grocery trips - so much easier.) Are there activities you can walk to, since you're prioritizing the stroller? Don't assume that you need to strap your kids into the car every single day and take them to the bank, grocery store, music class, doctor appointments, etc. Since you are here, you are already probably thinking of ways you can minimize your car travel. And as I recall, you were considering leaving work to stay at home for some period of time, so daily daycare trips might not be necessary? The point is that if you aren't doing a ton of car trips, it might be more worthwhile to look at getting 2 convertible seats and having a stroller that folds easily and just moving them in and out of the stroller when you need to have them out in the car. A couple other considerations - I don't know how much more space the rear facing convertibles take up so it might not help all that much. And I don't know what your climate is, if you're in Colorado or another place with cold winters, one plus to the carrier seats is that it allows you to get the infant all snuggled in before rushing them through cold air into the car. I am just posting all this to put another option out there - you don't NEED an infant carrier seat although there can be benefits to having them.
As for the stroller, I don't have twins but we have the Baby Jogger City Select with 2 seats and love it. With both seats in, it can get a little cumbersome to go over curbs, but it is narrow and fits through any doorway and doesn't consume the entire sidewalk. Which honestly isn't that big of a deal here in Denver but after living in NYC and getting pushed aside by wide strollers it was a priority for me :) Also, we don't have the car seat adapter and put our boys in the seat laid flat from a pretty early age, I would say a couple of weeks maybe, with lots of support around them. Something to think about. Again, it depends on what you are using it for.