Self isolation query

[iolaus]

Trying to work this out (I did search for an answer on PHE but couldn't find anything that quite defined it)

Person A diagnosed with covid on Monday (day 1) and was in close contact with person B the day before
Person B then self isolates, however on Friday (day 5) develops symptoms and gets tested - also positive - so self isolating for minimum of 10 days from Friday (so the following Monday - day 15)

Person B lives in a house with person C, they are trying to stay away from person B while all self isolating. If person C develops symptoms the following Thursday (day 11) and tests positive does person B still have to self isolate past the Monday or should it be 14 days from person C being positive?

Person B does their 10 days
Person C does their 10 days

Someone will put you up a chart I’m sure to show you, but if tested positive, the person isolates for the first 10 days after test, even if another person/s they live with gets a positive test, their incubation period will have passed during those first 10 days.

This chart?

but that chart was when we were assuming that you can only get it once then would be immune

Plus I was never convinced that just because child 2 didn't catch it off mum didn't mean he couldn't catch it from dad

It is still the existing advice though.
Ignore person A in your scenario as its only B and C that matter.
B gets symptoms on Friday so their 10 days starts and person C starts 14 day isolation
Person C gets symptoms on the Thursday which is 6 days after person B - they do their 10 day isolation