Annoyed 😑

So I understand all kids grow and learn at there own pace and parents teach the kids differntly. I'm not trying to be mean or anything so don't judge lol I have a 4 year old daughter my finances sister has a 7 year old son and 4 year old daughter there two months apart. But his niece doesn't know or understand anything!!! And it drives me crazy We still can't understand what she says when she talks and his mom and sister baby her so much it's rediculous . My daughter when she's over there house she'll dress his neice put her shoes on for her brushes her teeth gets her food! because she doesn't know how......his mom mainly watches her because his sister works but has no desire to teach her anything at all and I feel bad :/ and his sister just doesn't give a shit she gets home at a normal time too and rather do her own thing ... doesn't put her in anything but let's the son do stuff... And when all 3 are together no matter what he and my daughter are the ones getting yelled at because the niece doesn't no any better😑 they wana play with something they have to give it to her because she doesn't know any better... Total bs because she's the same age they just don't wana hear her cry over it 😡 my finace has said something and his mom tells him it's because she has a speical bond with her because she watches her everyday 😑