I'm mad that my boyfriend keeps giving our money to his siblings
Why do you have a problem with him giving his siblings money?
Because he keeps spending our money on them and we should use it on ourselves.
I understand being concerned about your boyfriend's finances, but you should try not to get too involved in issues between your boyfriend and his family. You are currently just dating him so he can use his money how he wants to. Now, if he is spending money you earned, then you have every right to be upset about that.
Well, I view it as our money because we are living together, but you're right that it's technically his money.
If it his money and what he is doing is not causing financial harm to himself, then you should let him do what he wants. If you are concerned about it, calmly talk to him and explain how you feel. If you explain it, he may see your point of view and consider saving more of his money.