Lol, if you think there’s something “common” about an 8 person family... not wanting to share a few photos, but literally wanting the EXACT same camera roll on all devices... ummm, I hate to break it to you; but the 1st thing I thought (or can imagine anyone else thinking), is “wow, that is super weird”.
Like there’s either some severe next-level co-dependency issues, deep knit into the entire family (very unhealthy), or... (probably a lot more likely), you’re an extreme control freak that imagines your family enjoys total lack of privacy, choice, & wants an identical camera roll on all 8 devices.
I can assure you... they do NOT.
If nobody has let you know that yet:
Work on communication too.
Maybe they’re scared to tell you?
There’s WAY too much to unpack in your story than to worry about iCloud storage!
I’m trying to imagine a world where an entire family has zero individual experiences & literally every single thing any of them experience is 100% communal with the entire family...
I guess cult members, living on a compound, that are disallowed communication with the outside world springs to mind... but I hardly think this could be “common”.