Guys,I need your help.

My mother bought two red ear sliders for my nephew when he was like 8. My nephew is now in his early teens and the problem is as follows.

My mother can be impulsive. I advised her against buying turtles as I know they are high maintenance and expensive. She can afford their care but is always busy. She bought the turtles anyway. Now the turtles have been growing of course and she is doing her best. She sizes up the tank when needed and they have uva and uvb lights. They have a lil minnow that lives with them and they don’t eat him even tho they could. They eat only pellets. (I’ve tried offering fruits and veggies, they refuse to eat them)

I recently moved back to my home town from 2000+ miles away. So I’m living at my mom’s. This is what brought the issue to light for me. They are in 75 gallon tank. And if it was one turtle she might be ok. But it’s not. They often get stuck and have to be rescued. They’ve taken to knocking their filters in the water and I feel it’s because they are cramped. They are each about 6 inches in diameter for their shell. I’ve told her it might be wise to consider building a pond outside since they are still babies and will keep growing. She is against that idea and is planning to move them up to a 100 gallon tank.

I just don’t think they’re gonna fit for long if at all. My nephew has begged to take them to his house but his mom wants nothing to do with them. Both my mom and my nephew have asked if I know anyone willing to take the turtles. I want the turtles. Mom is willing to house them until I have my own home to give them a pond.

How can I make their lives more comfortable until this happens??? What can I do to prepare to take them??? They deserve good care and I wanna do right by them. Both turtles are female (curved back claws) please advise

Or should I advise a sanctuary and call it quits???