Drop the co-writers, drop the 5th (and 6th?) live members, pick ONE producer, and start writing songs without trying to make them sound a certain way. Just let it come naturally. Every time a band tries to revert back to the way an older album sounded, it doesn't end up being very good. And I hope they don't try to write radio hits, because it obviously hasn't worked. Just try to write good songs, regardless of if you think they will do well on radio.
I don't know, Mayday Parade did it pretty well.
I don't know why everyone is so up in arms about the guitar player and Flyzik doing fills live. It isn't a big deal. Honestly. All Time Low can play their own music. So I wouldn't be worried about it. If it makes the show better (and I'm not justifying vocal backtracks or anything of the like) then who cares? Bands can write with more than one producer and still make a good record, too.