Hi, I had a cat that had a liter and she would move them wherever she wanted, because I wanted her to feel free to do what she thought was right. We respected each other. The first one that she would move out all the time turned out to be the one that clashed more with her personality as she grew up(probably the oldest). There was nothing wrong with that baby. The only thing that happened to that particular kitten is that I let her out one day. She was about 3 years old and decided to wonder off in the neighbors back yard where the dog caught her and chewed her up. She was my pride and joy. This killed me. ---Now maybe think about this. Maybe her Mom was telling me to look after her in another way, not because she was sick.
Anyway, don't think there is a health problem, unless there are other seeable signs from the kittens themselves.
----I just let my cats have the run. I love them so much. Now I tell them when they are infringing, but not unnecessarily. They are animals, but they are a part of your family.
--And I know ther is a possibility that you are going to give them away. But if you let the Mother do what she feels she needs to do, they wiill be more adjusted as pets. And hopefully the people that will recieve them are good to them.