I(35f) have 3 siblings. This story involves my younger sister(33f), who I’ll call Kayla, her husband,(34m), who I’ll call Mike, and their daughters, Emma(12f) and Kate(9f). [fake names]. Emma has juvenile ALS, a condition that is slowly killing her. She requires many care teams and around the clock supervision, and is in an out of hospitals for different tests and procedures. She was diagnosed at age 9, and there is no cure. Her disease has taken a strain on the whole family. Kayla quit a job she loved to look after her, and Mike has to work extremely long hours so that they can afford her medical bills. Kate was born 3 years after Emma. She was an accident, and Mike was furious when he found out she was a girl. Since the day she was born, I’ve stepped up as her primary caregiver. I moved in with them for Kate’s first year of life to look after her, and even after I moved out I enrolled her in all her extracurriculars, and drove her everywhere. After Emma was diagnosed with ALS, I basically became Kate’s mother. This relationship has created a very strong and special bond between me and Kate, and I love her more than anything in the world. Kayla, my sister, was grateful for everything I do for Kate, up until about 1 month ago. 3 months ago, 2 weeks after Emma’s 12th birthday, Emma’s doctor told us that he did not expect her to live past 13. This news shattered our family, and ever since then everything has revolved around making Emma as comfortable as she can be, and soaking in all the time with her before she passes. This news destroyed Kate. Kayla and Mike literally stopped interacting with her. She lives in their house, and they’re her parents, but it’s like she doesn’t exist. Her school teachers call me, telling me she has panic attacks at school and randomly starts crying. She never wants to be near Emma or her parents, quit gymnastics, a sport she loves, cut off friends, and doesn’t ever want to have a real conversation with me. These changes have greatly concerned me, and I talked to Kayla about them, but she told me that Kate has no reason to be sad, and she’s just acting up to take attention away from her sister. This really upset me. Last week Kate’s school had spring break, and my wife and I decided to take her on a trip to get her out of her house. This trip was amazing for her. After just 2 days away from her family, she seemed to magically turn back into her old self, and she started actually talking go me. It was amazing to see. It n the last day of the trip, I asked her why she had changed. She started crying and told me that she didn’t want Emma to die, but her parents were making her do everything for her, while treating Kate like she wasn’t a real person. They made her quit gymnastics, which I was paying for by the way, and told her she should stop hanging out with friends and focus on Emma. Then she asked me if I would let her live with me. I was so caught off guard by the question, but Kate was so Sad I knew I had to say yes. Over the past week I have been collecting evidence of how Kates parents have neglected her, and collected testimony from her teachers and friends. This morning I went to my sisters hours and presented her with the testimonies and bank statements, and asked her if Kate could stay with me. She exploded. She called me an A-hole for trying to take her daughter away from her and turning her against her family. She said I was a monster for trying to worsen her life during her time of suffering; and kicked me out. It’s only been an hour, and I’ve already gotten two calls from the school about Kate’s anxiety. Kayla won’t let me pick her up and see her. Kayla made a post about this situation on her private instagram account, and everyone is calling me and A-hole for even bringing the idea up. Here’s the thing. I think if I allow Kate to stay in her household it will slowly kill her. I tried asking nicely, but now I’m thinking of getting a lawyer to get temporary custody. What’s going to happen to her after Emma dies? Her parents hated her before Emma’s health got bad, I know she will continue to be neglected after. Plus, I’m already basically her mother, and doing all of the things her mom should be doing. However, I know if I do this I will probably lose all my family, regardless if I obtain custody of Kate or not, and I don’t want to further traumatize her. AITA for trying to take my niece away from her mother? And should I try to get custody?