Confusing options on the portal regarding unlimited plans

I have multiple mobile phone lines.

Two of the lines have unlimited data, the older pre-2024 type

I was exploring the xfinity mobile portal website and saw information about the new unlimited plans

https://www.xfinity.com/mobile/my-account/settings/level-move

At the bottom of the page all my lines listed with the dropdowns for 

-Unlimited

-Premium Unlimited

There's no option to stay on by-the-gig

So the website is not letting me switch my existing unlimited lines to the new unlimited plan. I am expected to make selection under all lines effectively switching all lines to unlimited.

QQ:

is it the requirement of the new plans that all lines must be unlimited data?

if not, how do I switch my existing unlimited lines to the new plan?