We've had that happen also, and the kittens did well. I think as long as they are all eating and gaining weight, they should be okay. Make sure that you weigh them every day though, you should be seeing almost an ounce every day, give or take a little. If it looks like one o more is not gaining weight, then I would consider an extra supplement either by tube feeding or syringe feeding. If the mother that had an operation is up to it, you may want to consider giving her 1 of her kittens and see if she will let it nurse. You have to make sure that she has the milk as well, so I cannot stress enough... weigh them daily.
You also must make sure that the mother feeding all those kittens is getting enough nutrition herself. You can get a good recipe for that in the health and nuetrition forum.
If there is anything else you need, let us know.