bad parents!!/need to rant

So, this is going to be long, but I need to vent! My brother and his wife live at my parents house with their two kids(4 & 5) I'm over there a lot so I know what's going on. I need to vent because it makes me so mad. My nephew just turned 5 yesterday and my brother and his wife did NOTHING for him for his birthday or any of his birthdays so far. (Every year my parents have small parties for both kids.) I just don't understand WHY the parents don't do anything for their own kids for their birthdays every year? For Christmas they didn't get either kid ANYTHING Because they think my parents and my sisters can just be the ones to buy them presents so they don't have to and the kids didn't get much at all, very little. My nephew asked me why Santa didn't bring him good things like other kids get and it broke my heart. I have my own son to provide for or I would have gotten the kids a bunch of presets. :(  My brother works full time and he doesn't spend any money on the kids. They haven't bought either kid clothes in 2 years or more. My mom keeps telling them THE KIDS NEED CLOTHES. They still don't buy them, so guess what? My parents and my sisters have to buy the kids clothes! It's getting so out of hand. So many times I've wanted to go off on them. I don't understand why someone wouldn't want to provide for their own kids! Like, why?? They just choose not to. I see how this is starting to stress my mom out since they all live with her and my dad, my mom does so much for them and for the household while my dad works, She has taken care of both kids a majority of the time since they've been born! Now my brother and his wife are talking about having another baby in a year but why would they if they don't even provide or do anything for the ones they already have? There's so much more I could say, this is only a tiny part of it.. I just don't know what to do at this point!