You are forgetting some things in your reflections. Pete and Monica have been married for a long time. We learn that in EP2. Ergo, it is likely that Josy and Tommy were still children. Josy is a daddy's girl and felt neglected by her father. She developed a hatred for Monica and Tommy.
I assume that's why Pete sent Josy to live with her mother. In the EP4 flashback, we learn that Josy went to another high school where she met Maya and Derek. But she wants to live with her father and spends the last year of high school with her father. She can decide that herself because she's already 18 by then. How do I know that? She's having sex with Maya, and in BaDIK, sex is only 18 and up, so we shouldn't forget that Maya was visiting Josy, which wouldn't have been necessary if they were still in the same high school.
So Tommy only met Josy as a child or young teenager. Probably only briefly, because Josy then lived with her mother for the time being. It's unlikely that Tommy had a crush on Josy, because they just didn't spend enough time together, and in the little time they did spend together, they will have been fighting for the most part.
Also, in EP2 Josy says to the MC that he now knows what you've been going through for years with Tommy.
I rather suspect that Tommy took his brother role too seriously and sabotaged Josy's dates or beat up the guys who got too close to Josy. Josy said herself that if Tommy knew she was dating the MC, Tommy would beat up the MC and Tommy would have the shortest fuse ever. But in EP6, the MC gets to slow Tommy down and put him in his place.