I am no expert on League play by all means. But I believe the max is 4 on a team in league play. The same 4 would have to play togther every time. If one person changes then it's as if you started a whole new league. If less than 4 play then you are ranking solo even though you are on the same team.
League play does not affect clan ranking at all. They are two separate things completely.
If I am incorrect on the first part then someone please correct me.