when introducing a new cat, they normall suggest putting it in a pet carrier in the same room as the home cat for a while over some days, maybe this would work for you. if the other cats are safe with the kitten, maybe put mum in a pet carrier and let her see her kitten is safe with them, do this daily for about 30 minutes a time and once or a few times a day, but dont let the baby out of her sight she will be very upset, if she cannot see her baby is safe. after a few days try and reintroduce them all again. im not very good at this sort of thing but i heard thats good to introduce a new cat, this may not work though as its her baby she is protecting. you may need to wait till the baby is older.