I have 2 cats right now, but had 3 up until last Christmas. Kedi, who is at RB now, got protective of any kitten that was new to the house (first Wylie then Rudy).
When Wylie was a kitten, he mothered him all the time. Then when we brought Rudy home as a kitten, he switched it to him. He also sometimes got upset with Wylie if he thought that he was playing too hard with Rudy.
He would watch for a bit, then he would actually (sometimes) go over to Wylie and swat him and start grooming little Rudy.

It was cute