This has been talked about for a while now, and I've never seen an explanation of what 'the rules' actually are - it's implied that it's supposed to be per 'household' (but obviously travelling is allowed) but then it says some of this is 'legitimate' being between 'family members'; so two related households are fine?

Honestly, it should just be that it's limited to people you're comfortable sharing the password with (total control of the account!) and the number of screens on your plan, as it is. I used to share with family and upgraded the plan when we used it more and found two concurrent streams wasn't enough.

They could remove all the content you are interested in overnight and you'd have absolutely no recourse other than stop paying next month.