Yes, both the UPPAbaby VISTA Toddler Seat and the RumbleSeat recline, including to a flat position for newborns or sleeping. When both seats are facing the parent, both kids can be in a fully-reclined position.
However, while the Toddler Seat features an adjustable footrest that helps position your child's legs for sitting and napping, the RumbleSeat does not have an adjustable footrest.