Referencing A movieClip within several after getting parent?

I have this MC attached to the stage with an instance of say: insA, then within this I have another called say: insB, then finally another one within insB called say: insC

so normally to access the third one I would use: insA.insB.insC do something.

I have this button within another MC called say: ‘2ndinsA’, so when a button within ‘2ndinsA’ is pressed I need to perform ‘something/move’ onto insC.

Now within the class attached to ‘2ndinsA’ i have the parent.getChildByName(“insA”) code and its seemed to grab the ‘insA’ and I could then move it, but its the insC that i want to move.

How can I then reference the ‘insC’ within that MC )‘insA’, i have tried several ways but all come up short (errors galore)

Many Thanks