it must be a very difficult situation. here are some guidelines:
if you live with others and you are the first in the household to have symptoms of coronavirus, then you must stay at home for 7 days, but all other household members who remain well must stay at home and not leave the house for 14 days. The 14-day period starts from the day when the first person in the house became ill.
for anyone else in the household who starts displaying symptoms, they need to stay at home for 7 days from when the symptoms appeared, regardless of what day they are on in the original 14 day isolation period.
it is likely that people living within a household will infect each other or be infected already. Staying at home for 14 days will greatly reduce the overall amount of infection the household could pass on to others in the community
if you can, move any vulnerable individuals (such as the elderly and those with underlying health conditions) out of your home, to stay with friends or family for the duration of the home isolation period.
if you cannot move vulnerable people out of your home, stay away from them as much as possible
To be honest, I don't think there's a great deal you can do - if you applied to court for an urgent order, the self isolation period would have passed, and even of not, the court wouldn't move him out when he'd been sharing with someone showing symptoms. I would say the best thing you can do is to speak to your son daily and if you are concerned that he's caught it, ring 111 straight away.