DH, DS and I all tested positive for Covid just before Christmas. DS2 fell ill a few days later and we didn't get him tested, because it was fairly clear it was Covid and because none of us were well enough to drive to a test centre (or indeed walk to the post box!)
He's now due to return to college and they are doing lateral flow tests, so as it's within 90 days he's likely to test positive and miss the first two weeks back.
We are doing asymptomatic testing in this area - if I take him for a test now, so that he can do his 10 days (again) before he goes back to college, will this mean that the rest of the family will also need to isolate, even though we know we've all had it?