I was just working on this 3 across issue last week. I'll need room for two infant seats and a toddler seat. I currently have a Graco Snugride and Britax Boulevard, but those really won't work well together with a 3rd seat. So, I worked through a couple different scenarios with the car seat guru at a specialty baby store in town.
They told me the narrowest infant seats were the Combi Shuttle or Cybex Aton.
The narrowest convertible chair is the Diono Radian.
We're going to end up using our Britax and getting two new infant seats for the twins. We thought about going straight to all Diono Radians to save cost of having to buy them down the road, but I really think we'll get use out of being able to transport the little ones in their car seats.
Even though the CRV has a LATCH system, we won't be able to utilize it and fit all 3 seats in. Everything will have to be seatbelted in, which the car seat guru informed me is just as safe as LATCH as long as properly installed.