Update:
Ficus doing well. Getting enough sun.

Concerned by Serissa. New green branches growing towards sunlight immediately after a few hours of being turned. But leaves are turning yellow and dropping. My sister is killing it with watering despite me telling her not to.

"Don't water it." I say as I leave the house for a few hours.
"Ok."
5 Hours later, I come home.
"WHY IS IT WATERLOGGED?"
"I watered it! "

Leaves are dropping off it as I type.

GrimThePanda wrote: Concerned by Serissa. New green branches growing towards sunlight immediately after a few hours of being turned. But leaves are turning yellow and dropping. My sister is killing it with watering despite me telling her not to.

Tell your sister you have consulted experts

But ermm... turning it? How often? Why?

" Moving the tree to a new position will stress the tree until it acclimatizes, on occasions causing yellowing and dropping leaves- this should be followed within a few days by fresh growth. "

I turn it every few days in place so that all the sides of the tree get sunned. I read somewhere that this was good, but I can stop if its stressing the tree.

GrimThePanda wrote: I turn it every few days in place so that all the sides of the tree get sunned. I read somewhere that this was good, but I can stop if its stressing the tree.

Here's a good care sheet:
www.bonsaitoolchest.com/download/Serissa.pdf

Stop turning it, at least until it's very healthy again.
Serissa's do not like wet feet, so review the watering schedule.