Orphan lambs can be a challenge to get to accept the bottle, it's usually a case of perseverance, and can take a week or more! I have three this year, and initially had to force them to take the teat - even then they would suck feebly or not at all and it would take ages to get 100ml into them. If they are reluctant then put a finger into the side of the mouth to open it, slide the teat in and hold it there but not so you are putting too much pressure on the nose.
With mine I was worried about them dropping off weight so put out some creep feed for them. One of the orphans was my own bred lamb who nearly died with hypothermia and by the time he'd recovered his mum wouldn't take him back, so he was the quickest to get the hang of suckling. Then another one suddenly developed a taste for it, but the third didn't seem interested - however, I kept offering it to her.
Now the three of them are like milking machines, they can't get enough or get it down fast enough!! They also eat grass and creep and I've had to stop the creep as two of them are beginning to look like blimps.
Re. the itching, do you mean just scratching themselves occasionally with their hind legs - most lambs do this. If it's all the time then I'd suspect some skin problem and probably best to get vet advice.