F15, I think you already know, but V1Driver does not use any iCloud space as you drive. Only when you do a backup.
How many pins do you have?
P.S. you could put those two iDevices on separate Apple ID's and they would get 5GB each. Then you can put them in the same family to share app purchases.
Only drawback with this is, in-App purchases are not shared. Grrrr. I understand why they do this (namely for buying tokens on games), but on Android in-App purchases were shared.
But it still may be cheaper than paying for more iCloud.
I wish Apple would give you 5GB per device (even if shared ID, that would be fair and encourage having more iDevices).