move from vzw to xm -- sharing 10gb plan and future phone upgrades?

I'm considering moving 5 phones from Verizon to Xfinity Mobile. I want to have all 5 phones on a 10gb shared "by the gig" plan. I read a very old post on a review forum that there were issues with this, specifically phones not working when not in proximity with each other.

Does anyone have experience sharing a by the gig plan?

Does xm offer upgrades? We will get 3 new phones and will want to upgrade the two byod phones in a year or two.

Thanks in advance for any advice.