The bubble is 3 families. None of whom can see anyone else.
So for instance my wife and I can see both sets of parents and no more. Both sets of parents cannot see anyone else either.
My brother cannot see our parents.
I guess banning any family meet up would simply end as a free for all...
I think it's about a proportionate balance. Being in a bubble of 3 families is exactly that. In my case it would mean my family, my parents and my wifes parents.
It means our family cant meet anyone else, my parents cant meet my sisters or brothers family, nor my wifes parents meeting anyone...