The guidance is not entirely clear and has changed

But I think the current guidance is that if someone in your household has one of the symptoms then whole house self isolates for 14 days. If you have symptoms you self isolate for 7 still. Clearly the two may come into conflict. In that case in absence of any guidance to contrary I am going with the family 14 (unless they live alone). The issue of course is partly as they havent been tested they may not have had it

If you live alone, self isolate for 7 days. If others in household, ALL of you self isolate for 14 days. This is because symptoms can take a while to show.  This is how I read it anyway. Hopefully someone else can clarify for you.

I believe that it is 7 days if you have had symptoms and 14 days for the rest of your family/household. I found these visuals helpful. As you say, the advice is constantly changing though.

www.bbc.co.uk/.../uk-51506729

assets.publishing.service.gov.uk/.../Stay_at_home_guidance_diagram.pdf

Hello, I've been advising employees 7 days inline with the NHS www.nhs.uk/.../