Potential Legal Dispute Over Cats

location: massachusetts, usa

hi there, and i was hoping to get some advice on this matter. i know nothing about civil/property law and google can only tell me so much.

i have two 4 year old cats. they were originally bought as family pets, but when i moved into my grandmother’s house 3 years ago, my mom agreed that i should take them with me. my partner (now ex - but we are still great friends) and i have financially supported them and cared for them for the last three years. we paid for their food, their vet bills, etc.

i moved to a different part of the state a couple weeks ago and my grandma agreed that i should take the cats with me. i had them both registered as my emotional support animals for my anxiety and depression because they significantly help these issues for me. my mother is now requesting that i return the cats to my grandma’s house since they are “not mine”. the cat’s adoption papers and microchips are in her name. my grandma is only in agreement to take them because she doesn’t want conflict between me and my mom to continue and mentioned that my mom is considering pursuing legal action if i don’t.

my friend (ex) and i are in agreement that we may have legal grounds to keep them since they haven’t actually been in my mother’s care for 3 years. i don’t have any idea if my mom will actually get a lawyer and try and get them back but they are something i’m willing to fight for if possible. i’m also curious as to how much my own lawyer would cost me if things came down to it. please let me know if this is possible or any advice you may have in general. thanks for reading :)