Have had a connecting cabin on the Majesty of the Seas this past summer. There was one door between cabins. The only difference I found between the connecting cabins and the other cabins in the same category was a loss of some drawers in the vanity. The vanity was shorter due to the placement of the door.
As far as sound . . . . we had my 2 and 4 year old grandkids in the adjoining cabin and found that we needed to crack the door at night in order to hear them when they got rowdy, couldn't hear them at all with the door closed (found this out the first night).
Definitely the way to go with kids.....2 bathrooms, 2 closets, 4 beds, a door, etc.