Good day. I have twin prem baby girls, 3 and half months old. Can they start teething so young? Signs are itchy gums, spit bubbles, drooling, chewing

Teething ??? A babies lips and oral cavity are lined with pleasure sensing nerve endings that help promote interest in feeding. It is a survival feature. I would not assume that their chewing/mouthing of objects means anything more. Little babies drool because they have no social conscience that drives them to hold it in.
Congratulations. That's very early be teething, but not anomalously so. Try giving them chilled teething ring for comfort. Call your Pediatrician or a Pediatric Dental Specialist, a Pedodontist, to see if an office visit is appropriate. And remember, 1st Dental Examination should coincide with 1st birthday.