Is it normal to sometimes play two notes with one finger? I am playing a song which requires my right hand to play A-B-E and B one octave higher at the same time. There is no way hand can do that unless I play A-B both with my first finger, the E with my second finger, and the other B with my fifth. Technique wise, is that okay?

yes. one example is Schumman's Traumerei, in a bar of the beginning section i remember i did exactly such a thing. however, i got bored with the piece and didn't finish it...

Yup, I've been playing the peice where the arranger specifically put in brackets to denote that I should use my thumb to press down two keys.