To interpret the OP's question, I perfectly agree with Yuuichi Tam's understanding of the background of the given phrases.
Yuuichi Tam said:
This sentence has some yakuza (Japanese Mafia) terms.
Yakuza treat their member as a family, so they use family words like 弟、兄, etc.
舎弟 is like a young brother for superior yakuza, 舎弟 call his superior yakuza 兄貴 or ～兄.
In my understanding, 舎弟 is a younger brother-in-yakuza's-law just like to say a younger brother-in-law who is not related by blood. Same as 舎弟, 兄 or 兄貴 is an elder brother-in-yakuza's-law in the given phrases.
In my answer I am going to call 哲也兄 "the boss Tetsuya" instead of "the elder brother-in-yakuza's-law Tetsuya", and am going call 舎弟 "an underling" instead of "a younger brother-in-yakuza's law".
I'm going to tell another reason why 兄 in 哲也兄 does not imply a real brother of the speaker B later on.
This phrase is an inversion of
こっちで implies こっちで勝手に, and こっちで literally means here and acutually it means from 哲也兄's side, and 勝手に means (to do something) without one's permission.
アレ is literally that, and in this phrase, it implies the man on the topic.
As a whole, the given sentence could be interpreted like:
Are you the man whom 哲也兄 boss Tetsuya made his 舎弟 underling by himself without your permission?
哲也兄！ ？ っていうか俺そういう扱いなの！？舎弟って、俺あのハゲに兄貴分らしい事何一つされてないんですけど！？
is roughly devided into two phrases:
- 哲也兄！ ？ っていうか俺そういう扱いなの！？舎弟って、
哲也兄！ What!? Is Tetsuya my boss!?
っていうか is と言｛い｝うか if I say in other words. そういう points to 舎弟って（＝ 舎弟という） in this phrase.
The phrase 1 is interpreted like:
What!? Is Tetsuya my boss!? He takes me for his underling!
ハゲ is a word to be used to insult a person who is bald. In this phrase Tetsuya seems bald.
The whole meaning of 2 is like:
I haven't been given anything that seems a favor from a boss from the bald bastard, (so I wouldn't like to consider Tetsuya is my boss).
The final answer:
I think Tetsuya is not the speaker B's or her older brother but is also her boss or something like that, because the speaker A called Tetsuya ハゲ in her presence. You can't insult a yakuza in the presence of his real sister even if the speaker A does not accept himself as an underling of Tetsuya.