The mods on the EN forums are notoriously poor at interpreting the rules. as others said, this has been confirmed years ago to be a copy&paste error from other inno games.
It's all about preventing you from getting free "diamonds" for inviting [yourself] to play the game: a feature that doesn't exist in Elvenar.
If it actually was about fellowship invites
1. the ultra-simple workaround would just be to ask a fellowship member to invite your spouse.
2. the rule should simply state that
"you can't share a fellowship with your spouse/ip address":, the "invite feature" mentioned makes no sense if it pertains to FS
@helya could you ask for an official statement on this, please?
"Members of the same household using the same IP address may play together in a Fellowship provided that they do not break the No Pushing rule" - someone official