My girls have been Prius babes since they were very little. We did have bucket seats in the prius, then britax marathons, and now britax boosters. It certainly can be done. Not with an adult between them. The only issue we had with the prius was getting strollers in the back, and only for the jogging stroller.
Logistics are not nearly as hard as they seem before the babes come. Bucket seats are great for the first few months, especially if you get a double snap n go! But babes grow out of the buckets surprisingly early - at least mine did. Glad we got ours used, and we still re-sold them.