How do i stop my mom from buying this hamster?

My sister has been complaining & crying & whining & screaming about getting a hamster for like a week, last hamster she had she left it in its ball to roam around the house & the dog killed it. Plus she drowned my guinea pig. :( If she gets the hamster i’m going to end up taking care of it, which i donnnnnnnnn’t want, i ended up doing the same thing wif her mice. I already told her if she’s getting it it’s gonna end up getting killed, she’s not gonna take care of it like she did wif her mice, i’m not sharing my food & bedding wif her, & yet my moms still getting it. My dad has clearly said NO to it like a million times, but my moms just getting it so she stops whining. It makes me mad though, i asked my dad for something & he said no so i went to my mom, she said no, then when my sister does it & asks my dad he says no, she goes to my mom who also says no but still gets it. I haaaaate siblings. -.- ayfhkdsjfkasjdlfjs. Their going to get it today, i need help convincing my mom not to get it. When i talk to her about it she will be like “NO KRISTA WE’RE NOT TALKING ABOUT THIS AGAIN.” (yes i nagg her about it constantly. |: ) & then she will hang up. I’m gonna get in trouble wif my dad if she gets it. /: Help ? I’m confusing. Thankks.