Room sharing means a baby sleeps in the same room as their parents, but on their own separate sleep surface such as a cot or crib. It is not the same as bed sharing, where a baby is on the same surface as an adult. Safer sleep guidance recommends room sharing on a separate surface for at least the first six months.
For twin parents, room sharing carries a second meaning: the two babies sharing a room with each other. This is common and generally works well, though in the early weeks twins can wake one another until they get used to the other's noise.
Whatever the arrangement, the sleep surface and setup for each baby should follow current safer sleep advice from a source like the Lullaby Trust.