Bubble Question

[Notasyoungasiwas]

I've been quite up on rules etc but keep reading conflicting info on the following:
A lives with B
A is clinically extremely vulnerable
Can A form a support bubble with C and D from another household? A does not require care. (I know the rules on single adults forming a bubble and have read up on CEV people forming bubbles but I can't find anything about CEV people HAVING to live alone to form a bubble) Hope that makes sense

You can only bubble where one household has a single adult in it. There is a childcare bubble but it’s meant to be drop and collect only no socialising.

Thank you *icecream