First of all: you're an ass because you stole my avatar.

Secondly: you're not an ass because you got her sister to like you. Congratulations.

Also, why can't you just have an orgy with both of them? I was in the same situation once. I was with a girl my age and her older sister by nearly 3 years was crazy about me. She ended up blowing me under her sister's bed XD

Don't worry about it man, you're making this too big of a drama, just let everything go. Maybe talk to Andrea about it, but otherwise, don't worry.

At least now you can pick ^_^