I got Apple One Unlimited, and I activated Apple One for my line. It's active on my phone, no problem there. The Verizon web site says I am signed up for Apple One Family.
If I try to activate another of my family's lines, it says that I have to unenroll from my individual plan first before I can enroll in a family plan. (Remember, the web site says I am already enrolled in a family plan.) If I do that, now Apple One is active on my family member's line but not on mine any more. If I then try to activate another line, I get the same message that I must unenroll them from their individual account before I can enroll in a family account.
I can find no way to activate Apple One on more than one of our lines. If I look on the phone itself under the Apple One subscription, it says that is administered through my Verizon account.
I upgraded to this plan specifically to get Apple One for my whole family.