Keep mobile eligibiilty while moving internet service address

I would like to cancel my Xfinity internet service at my home and take advantage of faster, cheaper fiber connection I now have available, but realize that would likely result in a $25 per line surcharge if I kept Xfinity Mobile plan. My son just moved away from home (he is a member of my mobile plan) and established Xfinity internet at his new address. I want to know the easiest way to have his plan provide the eligibility for mobile discounted service?