First of all, Pedro is not TECHNICALLY a prince, I know that. He thinks that he's a prince, when logically he isn't. This is just an inside joke like Trixie calls herself Great and Powerful rather than Trixie. Secondly, I will make him more masculine, I agree. Thirdly, he is logical a royal pet, but since my OC has Asperger's syndrome and Pedro talks, my OC calls him a brother because they share a close relationship and they both act like brother and sister rather than master and pet. I hope that cleared things.
The whole 'adopted brother' thing is just my OC, Harmony Star's and Pedro's relationship. They act like siblings because since he can talk like a normal person and he is adopted by Harmony because she was a filly when she adopted him and they may be different species but they can be siblings if they want to.