I'd be curious to hear about the room situation too - we're doing 2 rooms; my daughters are 18 & 17 (at time of travel) and the ABD Reservation Agent told us to do 2 because the rooms are small and the overall price would be the same for 1 v 2 rooms. Not to mention, 2 bathrooms would be helpful.
When we did Imperial Cities, we booked a double and a triple, and they were connecting in all three hotels. It was really great. I know that some of the families with us on Viva had little apartment-type rooms that were just lovely!
This is probably info you already know, but for Roma and La Costa Bella, the info is as follows:
Notes on Accommodations: (subject to availability)
Parties of three in Rome and Sorrento are accommodated in one room with a rollaway and either one queen bed or two twin beds.
Parties of four booked as a quad:
Parties of four having more than two Guests over the age of 12 are accommodated in two connecting rooms, each having either two twin beds or one queen bed.
All other quads in Rome are accommodated in one room with two rollaways and either one queen bed or two twin beds.
All other quads in Sorrento are accommodated in one room with one queen bed and either two or three twin beds.
Parties of four booked as two doubles are accommodated in two double rooms, each having either two twin beds or one queen bed.