I do the same but do pry the mouth open, squirt a little in their mouth, release them, they taste that and get interested. I then tickle their tail head area and they want it all the more, trying to look for it. I repeat until they are really eager, then, from the back of the udder area, hold the teat upward so they find it better and latch on. Tickle the tail head at the same time. Also you can get a 12 cc syringe and feed colostrum that way at first, feed it slowly at the back corner of their mouths at the same time, insert you index finger in the mouth move it slightly in and out still leaving it inside the mouth, after a while, this should trigger the suck reflex, feed another 12 cc's and if you get that reflex then put them on the teat and do as I described above.
If they still do not get the suck reflex they may need a small Bo-Se shot.