These babies are probably old enough (they do appear to have teeth) to have regular canned cat food - so go ahead and open a can, mix it with a little warm water and put it down for them - my bet is that they will eat it.
The kittens should stay with you and not be stressed out in any way. You don't want to spray these babies for fleas- talk to a vet about safe flea treatment- anything brought over the counter could potentially harm, even kill these babies.
Do not put them back with mom, if she is feral she will either ignore them or try to kill them if your scent is strong on them, and seeing you have had them on your lap, I would guess it is. Bathing them to get your scent off of them won't work either, they will smell differently and she will want nothing to do with them.
is set up to help you here.