Only available on EE as far as I know currently although O2 do offer sharing it needs to be set up at the start of all contracts that want to share data and calls etc.
https://www.o2.co.uk/sharer-plans
I have no affiliation whatsoever with O2 or any subsidiary companies. Comments posted are entirely of my own opinion.
This is not Customer Service so we are unable to help with account specific issues.Currently using:
Pixel 7a (O2 & Lyca), One Plus 6 (Sfr), iPhone 12 Pro Max (Vodafone)