Ideally you should've started introducing the kittens to wet food at around 5 weeks and between 6-8 weeks the mama cat should've had them weaned. They will be getting their adult teeth soon and could do some serious damage to mom's teats.
If she still hasn't weaned them in a couple weeks, separate the kittens, give them wet food and take mom in to get spayed. Her maternal instincts are obviously not fantastic, and the world doesn't need more kittens. She can get pregnant again at any time so please don't wait to get her spayed.

