3N-2-2-2-1 butterfly is legal. It seems to meet all the requirements. 3W-2-2-2-1 butterfly is illegal because there are 3 players on flanks.
-------ST--------
AML----------AMR
----MC----MC-----
DML----------DMR
----DC-DC-DC----
4-2-2-2 butterfly is illegal, because there are no striker, and there are 3 players on both flanks.
----------------
AML--------AMR
----MC--MC----
DML--------DMR
DL---DC--DC-DR