Car seat decisions.

So we got a double stroller when we had my second cause my first was 16 months. We are now expecting twins and I was gonna get new carrier car seats that go with our double stroller, we just used the one from our first even though it didn't match the stroller before. We intend to baby wear a lot because I like it, it's easier and my second son is "high maintenance" and won't nicely hold a hand or walk by a stroller. So my question is do you think we can get away with just getting the convertible car seats? I'm worried babies will be too little to make them work, or should we just get the carrier ones? I know they make pads and stuff to help little guys fit better, my first was premie but I had never considered trying to go right with the convertible seat.