It's the only way you'll be able to share data unless they can change your tariff on the new sim?
Maybe worth asking them, otherwise, you'll be stuck with tethering when in the same room as the other phone.
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)