The longer they are with Mama, the more well adjusted they'll be. When Mattie Grace and her babies were with me, I didn't let them go till they were at least 9 weeks old. Mama's milk will dry up once they stop nursing.

The best way to wean them, is to mix KMR with a premium canned kitten food so it's diluted into a paste. Put some on your finger and offer it to the kittens. They should go crazy for it, and believe me, it gets ugly. They make a mess but it is so worth it.