It really doesn't work like that, Guidance is not and never can be the law when it conflicts with what the law says.
Take a separate issue in special educational needs law. The guidance is the Code of Practice which says that an Education, Health and Care Plan must name a school or type of school to be attended by the child. In relation to cases where it is accepted that a child can't attend a school and needs home tuition, the tribunals (equivalent to courts for SEN purposes) held that a school or type of school had to be named even when it was fully accepted that the child was never going to school. Then everyone had a close look at the regulations, noted that what they actually said - in contrast to the guidance - was that a school/type of school only had to be named if it was appropriate, and it was held by the Upper Tribunal that if no school was appropriate then the relevant section of EHC Plans should just be left blank with home tuition arrangements being set out elsewhere in the EHC Plan. However, the guidance still says that a school/type of school must be named.
If we are to follow what @MRex says, the guidance trumps what the law actually says and the Upper Tribunal has got it wrong. But that cannot be so, not least because the law as passed by Parliament doesn't say what the guidance says.
And that's the situation here. No matter what the respective duties are in relation to indoors and outdoors, the fact remains that what is prohibited is a gathering of more than six, and if there are seven people in a building two of whom never interact with the other five then all concerned are acting lawfully.
For what it's worth, even the guidance isn't as dogmatic as you suggest. It talks about groups of six, not just six people. So even under the guidance, you can have one group of two and another group of five in the same house and that complies with the rules if they are separate.