This is unfortunately a position new rabbit owners find themselves in often. Mis-sexed rabbits that reproduce once they sexually mature.

If you can, do try get them feeding from the Mum. Can you have someone hold her then you can hold each kit to a tear underneath?
If you can get them to suckle, it will help her produce milk if she hadn’t already. It’s really important they get the colostrum in the first feeds.

If this is not successful, you could ask around if anyone had a nursing mum they could be fostered to. There are likely some as it’s nearing Easter and some breeders like to have rabbits ready to be sold by then so they’d be born around this time.

This is worth a read if you haven’t seen it before:
http://www.bio.miami.edu/hare/surpriselitter.html

This one relates more to rearing orphans: http://www.bio.miami.edu/hare/orphan.html

It’s great that you’ve kept the 2 survivors alive this long. Well done!

I’m not sure what is happening when they put the head back & gasp. It may be the milk is going too fast.
We usually recommend folks in your situation seek advice from Rabbits Online forum as there are more members experienced with infant rabbits on there.
http://www.rabbitsonline.net

First: you need to separate them if they aren’t already. Your female can get pregnant again immediately after giving birth, which can be dangerous to her depending on her age.
Second: I would cut out the heavy cream and just do KMR. Whipping cream could upset their very fragile tummies. You can check out rabbitsonline as they have an area dedicated to breeding, so maybe one of the breeders on there could help you.
Third: Make sure they are completely separated until 1-2 months after they’ve been fixed, then you can go through the proper bonding process. You can read about that in the INFO section under bonding. Your male can still produce semen for up to one month after his surgery.