Urgent Splayed legs three weeks old parakeet

[Han]

Hi, I am Han and I am very new to splayed legs three weeks old parakeet. We thought that there are only two new born chicks. We were afraid to check the nest box because the mom is very aggressive. She bites the male if he is even looking at the nest box. Four days ago she started attacking him. We removed her. We realized that there are three chicks in the nest box. The youngest has splayed legs. It has almost all of its feather. I took the nest box away because I was afraid that the older and healthy siblings would step on it. They are on a flat floor cage. The male bird, Stardew has been feeding them very good. However, today I noticed that he fed the splayed legs baby less compare to the others siblings. I tried the vet tape on the splayed legs bird. Should I move it to be with his mom so she would feed him or should I move the other healthy siblings in with her? Her name is Sweet pea. Thank you.