Four weeks is young for kittens to be fully weaned. Keep trying, but they will be more ready to lap milk and eat soft food at 5-6 weeks. [emoji]128522[/emoji]
they have no problems eating soft food they love it as for drinking they know how to lick milk, bet rarely do problem is that they also chew nipples and sucks to buy new ones all the time..
If they are eating soft food only (no dry), they are likely getting plenty of fluids from that. Taking milk from the bottle is more of a comfort thing, though certainly is beneficial with getting extra calories in them.
As for the nipple, yes, the kittens are teething and the nipple feels good to their mouths. Try getting them some teething toys. These are good options: