The sharing component for the two main girls is ONLY with women (mostly each other) with one exception.
Episode 4 will have a choice that can lead to a sharing scenario with men for one of them - however, this is a bad choice and will result in a GAME OVER - a bad "ending." You do not have to choose it. It is there mostly for the satisfaction of the results for denying it.
Non-main girls may (depending on who they are) have MMF scenes in the future.