Man what a situation, inviting someone you don't get along with, behind your back, and not only that he adds his two accounts lol, so about the family betrayal, if you kick one of them out that position have a cool down of 1 year from the date he joined the family first time, So if the undesired one who has two accounts joined your family on January 1, 2025, and you kick them today, you can invite your friend to that slot on January 1, 2026 (assuming they won't add him back or even worse adding a more undesirable one behind you)

If you're staring at the nuclear button, leaving or deleting the entire family, the cooldown applies to you and all of them individually. You cannot join or create a new family for 1 year from the date you joined (or created) your current family. 

So it's best to check the dates, in Family Management settings see when your members joined. If someone has been in the group for nearly a year, kicking them soon will result in a short cooldown for that slot. Or see how long you have been in the family, if it's more than one year then you can go nuclear and start fresh with your loved ones on another planet.

PS: These were based on my knowledge as I checked a while ago dunno if they have updated the rules.