<human>: Bit of backstory:
His brother has a wife and 3 children and we rent a basement apartment under their home. 

My boyfriend and I have some money troubles. He is the main provider because I only work part-time(our rent is really low so we don't have much cost) but my BF has a lot of debt due to school and other personal events. We use our visas a lot just to get by. 
His brother is a waiter so he makes crappy money per hour but has generous tips and his wife has a stable job as well. But they are moochers. I didn't know this before we moved in.

My BF is the type to lend money or his visa to his family if they need it, but rarely gets paid back. His brother has done this many times. He also has my BF buying him cigarettes on occasion, beer, take out... It even comes to a point where they will come downstairs and take beer if they're out or milk for the kids. We have even paid for camping trips/supplies ($500) and other trips/food ($200+)

I lost it this morning when I heard them come downstairs and take cat food out of our 30$ bag and fill their container for their food.
I told my boyfriend this and got very little response. I mentioned it more about how he bought the bag but theyre just coming and taking half which is ridiculous. He got angry with me for talking about it and has stopped replying. He gets upset over money and debts but still takes this kind of crap from his family. His brother needs to stop stepping on him but my BF also needs to stand up and say no or ask for his money back.
We get in fights over money which affects our relationship and he just sits by and lets all this happen cause "they're family" 

Is there anyway I could convince him to step up and say something? Any tips or thoughts you may have would be awesome.

Can you provide a brief overview of the text?
<bot>: BFs brother takes money/items from him, doesn't pay back, Our money problems affecting relationship but he won't do anything about it. Help.