I think it would be cool to invite some your companions to the faction you are currently in except the ones that are already in the faction

"Hello Danse, would you like to join the Railroad?"

hmmm...

Did you read the OP? He said so long as they're not part of another faction.

well i like they are consider settler, so u can give them jobs when u arent using them.

Yeah true but i just think it would be so cool like either way they can give you missions but like the minutemen or railroad once you become a higher rank in that faction you are able to invite people who are not in a faction to join the faction that you choose to join and then train them and promote them if you wish but still have them as a companion and still take on missions together