User blog comment:IamJakuhoRaikoben/Chapter 468: Memory of the Stars, Review./@comment-24499036-20160109212259/@comment-24546844-20160109220645

And that is the reason why I only used loyal to describle Invel.

Can you really picture those two being moved by the Power of Friendship and joining FT? By your own description, which I completelly agree with, both of them are in the perfect place, a beligerant country involved in a big war. It was said that Zeref had to keep them in line, or something like that. A pacific guild like FT, and we can even count Fiore as a whole I guess, has nothing that would interest them so no, even if they're not loyal to Zeref or Alvarez they wouldn't want to join anything that prevent them from being themselves. They'd probably just go around stomping things till they find a purpose to live/fight for.