Traveller returning from overseas to UK

[MollyButton]

I've hunted the government websites but can't get the answer, and this will affect if I have to re-arrange our house.
My DD is returning from overseas. She has been told she will have to be "quarantined" for 14 days.

What I want to know is? Do we as a household have to self -isolate for 14 days? Or does she have to self-isolate within the house for 14 days? Or what?
If she has to self isolate - I may have to move her to my bedroom (she has the smallest and it would be awful for her mental health to be cooped up in there).
If we all have to self-isolate that would have a knock on effect for my DS who at present still goes out to work.

Any help gratefully received.