It wasn't experimenting because you didn't chose to do these things. An older child was ordering you to do these things and this is what makes it sexual abuse. Experimenting is when 2 equals are both choosing to experiment.

I could see how this would still affect you because this was a loss of empowerment for you and boundary violations. To be beaten on numerous occasions at this house without any protection would be traumatic too. You write you have self worth issues, this certainly would affect your self worth because you would have been thinking while you were being beaten and not being protected that you must have been worthless (you weren't, these people were dysfunctional but you still would have thought this).