That rule about not being allowed to invite players from your household is not referring to fellowships but rather the game itself.
You see,
other inno games have a "refer a friend" system that gives you premium currency (diamonds) for inviting friends to play. Obviously, the easiest way to scam diamonds would then be to invite "your wife/kid/dog" and get those rewards. To help curtail this there is a rule that you can't get referral rewards from the same household.
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It's a shame that the original player seems to have been driven away by this confusion (they haven't visited the forums since), but it's understandable- I mean who wouldn't want to play with their loved ones? I know my wife got me interested in it 6 years ago and we never would have played for more than a week if we'd been forbidden from playing together.
Hopefully with this clarification it won't happen again.