Unsure. The Christmas rules don’t seem to mention overnight stays apart from in the context of forming bubbles and mixing in private homes.
If you look at the new tier rules it seems tier 2 (where we are going; Norfolk) is fine. Your parents are not allowed overnight stays outside their local...
You can choose to follow more stringent rules as ultimately safety is a personal choice. I think the point being made is that many will not do so and the four Governments have at least provided a framework around which most will agree, as an alternative to a mass refusal to co-operate free for all.
But the numbers of COVID cases in schools would suggest otherwise. Infected kids have been spreading the virus within families and to teaching staff. I don’t disagree that choices have had to be made but keeping schools open has co-incided with the second wave and that decision will have cost...
Yes, we will follow the rules just like we observe the unenforceable (in the countryside) drink drive laws. We have a COVID case in our extended family. You may have as well without realizing.