there are various tricks farmers will swear by, re bottling a lamb. Id suggest try not to get too aggitated: it can be frustrating when all you are doing it trying to help them and they just clamo on the teat and wont suck!
I had one wildy i found abandoned and she wouldnt drink for a few days, then just as i was getting desperate i introduced her to my other sheep and she immediately wanted to suckle- so i grabbed her and put the rubber teat in her mouth and presto!
I would suggest (if you havent already) tried bottling in a natural position, ie lamb stood up not lying in your lap, using your arms or hands to partially cover the eyes to emulate the "under the back legs" feeling. I tend to find that works if the lamb is between your legs and facing away from you. Make sure milk isnt cold or too hot (blood temp is right) dont be encouraged to widen the teat hole as if not sucking they will choke, but you can squeeze the teat sides whn it is in the lambs mouth to squirt some drops in, also tickling the throat to encourage swallowing, and finally rubbing their bum (mom would sniff their bum when suckling to make sure its their baby back there.
Another trick if they are clamping on is to try pulling the teat slowly out their mouth.....
good luck and keep perservering, im sure you will all make it just fine in the end!