If I understand your situation correctly, you want an attached actor (a child of some other parent actor) to generate collisions? This is not supported by the engine, as far as I know. The child actors do not perform a “sweep” when moving, so they do not detect collisions.
I have a very basic fix for this in C++, here:
Sorry that doesn’t help much if you’re working with blueprints. Epic is aware of the issue and has said in a few posts on the AnswerHub that they are “considering” a fix.