What should we do?

We're having to rearrange carseats and want some input. We have a '97 Chevy venture, the sport edition. This has five bucket seats in the back, three in the 2nd row and two in the 3rd row. We've had all three kids in the 2nd row, Rosie in the middle in her infant seats and the boys on the outside in the integrated child seat. Well, the seatbelt on the middle seat has never been entirely cooperative, and has now broken completely, so at least one of the kids will have to go in the back and we'll remove the middle seat. I'm not sure how we'll handle loading and unloading with this set up. When we went to the with Rosa and Lily we had Pauly in the back with a booster seat, but I had to open the rear hatch to buckle him in. We have the infant seat, a Fisher Price Safe Embrace Convertible, a Graco Ultra Cargo (or whatever) combination seat, and a Cosco low back booster. Two of the seats have integrated child safety seats. Pauly is 37lbs, Roger is 27lbs, and Rosie has to stay rearfacing regardless. Where would you put them, and why?