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