How to deal with spoilt nieces...

I have three aged 10, 4 an two and I can't handle their attitudes. I look after them majority of the time, the eldest one is so rude to me, she glares at me when I tell her what to do, she's lazy, selfish, she tries to tell me what to do, she bullies her sister's, she's arrogant (she's teaching the younger two bad examples) like I don't put up with it I growl her but she does not care and I'm really starting to resent her. Her mom's no help at all, she doesn't put up with her attitude as such, nor does she encourage their bad behaviour, but she doesn't discipline them. At all. She will threaten to hit them if they don't stop. But I can't do that with the older one. She's just rude and narcissistic and I just want to yell at her.