Kitten! I need help!?

My little brother found a kitten outside, I know mother cats putvthem places to go hunt etc. But my neighbor has a mother cat and the babies are just about a week younger than the one he found. I was wanting to know if the mother will take in the kitten. And how old they have to be to sell them. I'm NOT NOT selling the cutie. I'm giving him to my bff cuz my cat is completely territorial. Unless there's a way they could get along. My cats female, also had a litter but we kept one and after she weened it she was soooo mean to it. The kitten is about 1 month old, its eyes are just almost all the way opened. Its also a boy if that helps. Please help me, i'd sooooo apreciate it!