How to deal with family?

my little niece is 10 years old and she is not getting enough attention from our family her Nanna is only caring more about her 2 year old granddaughter than she is 10 year old Kim let me tell you about each one of them and see if you can help me out i look after her now like a parent and no older adults are listening to either one of us so Kim she is a fun girl so adorable she gets mad like everyone else in the world but then she gets over it quick she is sporty a dancer and cares about the earth and other people. Now Addison she is a spoiled brat she wants to be held allll the time and she weighs double what she is so post to weigh and double the height, she is not fun to be around even her mom is not her dad OMG he is a trashy crap head she has a good house and Kim lives in an apartment so, Kim gets so mad at her she comes to me and cries all day thinking no one except me God and jesus loves her i hate to see her like that please help PS. Addison is so fat and ugly she says