Watching Travelers (2016) reminded me of this bit from Robot Chicken that is mocking the Battlestar Galactica reboot and how so many characters were eventually revealed to be cylons. It sort of seemed like the writers of Travelers had used "just make the character a traveler" as an excuse to help whenever they had written themselves into a corner or something.

Aside from the characters who were pretty much always travelers, this is who I can think of off the top of my head:

Robot Chicken S4E1 "Help Me": https://www.youtube.com/watch?v=FzH6GVBSXSk

Been a while since I rewatched it. These are all the main mission crew set up at the start of the show though? I don’t remember the bottom left lady, is she the captains hosts wife? and I don’t remember the social worker getting taken over unless it was part of the blood vault episode which I think that timeline was overwritten.

Not everyone pictured on the dartboard there fits the "suddenly a traveler now" trope, just like how in the original bit, not everyone pictured on the dartboard was a cylon. It's just everyone from this cast photo:

That's the five main crew (who became travelers right at the beginning of the pilot) plus the social worker.

There was a fan theory out there before the finale that Cylonism was an STD I believe.

How did the ship operate when half the crew were Cylons? They weren't Cylons yet!

Then everyone started going with the theories that all of galactic history was Cylons all the way down which is less fun but just as stupid.