6-7 week old kittens won’t eat

So my mom is a cat foster and she recently got this white female cat that had two other kittens one male and one female and the first day we got them I had them situated in my room. Everything was fine for a couple of days the mom was very nice and she liked to be petted as well as the kittens however after a few days she started rejecting the kittens really hard she would start to hiss at them every time they got near her so she basically stopped feeding them so it eventually got to a point where we had to separate the mom from the kittens because I think she started hitting them in the night while I was sleeping however I get the feeling that the kittens are very sad that their mom is no longer with them and it’s been like 2 days since we’ve separated the mom from them and they just refuse to eat. I think they’re about 6-7 weeks old and I’ve been trying to get them wet food but they just look at it and turn away without even smelling it or anything so I’m worried they’ll become malnourished so at this point I’m debating getting kitten formula for them but if you guys have any advice it would be helpful