I have an older, disabled female budgie named Bethany. She can't grip, or fly, and has trouble reaching around to preen her oil gland. I have another female parakeet named Molly who is about the same age and has mild feet issues. Both see a great avian vet regularly.
This past winter, Molly's behavior toward Bethany has changed into one of maternal protection. They have been cuddling a ton (like one sleeps resting their head on the others back even), Molly will preen Bethany often from head to preening gland, and if I try to pick Bethany up to check on her, Molly makes a threatening noise at me and tries to bite me.

This is a little confusing, because Molly often acts like she is taken care of a baby although both of them are middle age. Another thing Molly has been doing is regurgitating / feeding Bethany. And I just noticed that Bethany has a large squishy crop under her feathers and looks a bit like a bullfrog. She definitely weighs more than normal.

I need to get Molly to stop feeding Bethany, but I'm not really sure how. Should I separate them? Molly has always been good about taking care of Bethany's feathers so I would hate to deprive her of that as well.
I think part of the problem is their favorite place to hang out is a padded wooden ledge in the corner of the cage. I think it's making Molly a little bit nesty. So I'm going to remove that, but other advice will be helpful!! Thank you.