Over-Groomin

I have two kittens, one is around 7 months and the other is 14 weeks old. The older baby grooms the younger and I think she's over-grooming around his eyes. I'm noticing some missing fur right underneatht his yes and it's got me a little worried.

Anyone else ever see this? And does anyone have any idea how to stop it?

I have a 6 year old female cat that cleans herself excessively. Its mostly her back legs and her belly. She is all bald and it looks like someone has shaved her. I have no idea why she cleans so much. I thought at first it was food allergies but I notice her cleaning almost constantly. She is always cleaning my other cats, and tries to lick my hands, arms, and face also. Is it kitty OCD?