AITA for refusing to pay for my son's stepbrother to play hockey alongside him while also refusing to pull my son from hockey?

I have a 7 year old son with my ex-girlfriend. She left me when our son was 4 months old for her husband. He has a son 7 months older than mine. My ex is raising her husband's son as her own, because his bio mom is not in his life, and this is a point they have argued with me. Because of the way our relationship ended we are not on the best of terms. And because my son is closer to me than to my ex or her husband it causes more trouble when I do something for my son. They think I'm buying him when that's not it. Nothing I do is about buying my son or making me the favorite. I just want to provide a good life for my only kid.

My son had expressed an interest in hockey for a while and several months ago I signed him up for some lessons and now he's part of a team. His stepbrother doesn't get to go and he's jealous. My ex and her husband can't afford to send him and so my son doesn't go on his mom's time. But this is no longer enough and because his stepbrother is aware he plays hockey, my ex and her husband told me I need to either pay for both to play or I need to pull my son.

My ex's husband told me his son does not need to have his disadvantage flaunted and with them being in the same school he does hear about it. He told me his son deserves to feel equal to his sibling. My ex made the same argument. She said both kids are being raised as hers, so they're half brothers in the eyes of the family and she said that means they should be treated the same. I told her in their house, by their families this is true. But I am not in their house or their family.

I refused to discuss it after telling them no to paying for the stepbrother and no to pulling my son. They went a little insane over it and accused me again of buying my son's love.

AITA?