According to Ian Nicolson: The minimum dimensions of a man's berth should be;
Width at shoulders and hips- 1'9"
Width at foot-1'1"
Width at Head-1'4"
In my opinion it all depends on your space allotted. Generally if there is a two person berth already, the best you are going to achieve on a refit
of any type is... two people. Most builders do not allot excess space when placing berths. Trying to jam 3 or 4 in same space does not cut it if journeys are more than a weekend.
Two boats will keep the peace, related or not.