Christa and Omid replaced Carley and Doug
 

Carley and Doug were both dead by the time that th group met Christa and Omid, but I think they were the replacements for them. Carley was a strong female presence, level-headed and passionate. These traits all describe Christa. Doug was a lighthearted fellow, funny, and had ingenuity. Omid was all of these things (he says they made it as far as they had because of Omid's "scrapper" skills, indicating he's got some ingenuity floating around. And it was made clear Doug and Carley liked eachother, and here it shows these two identical personalities wound up together as well.

That's funny, I thought of that exact same idea like a minute ago and considered making a thread about it. I even think your comment made me think about it:
Carley and Christa really do have similar subtitle colors too.

More or less. I still prefer Doug and Carley. We know nothing about Christa and Omid.

We know they had a cat. Said cat is 'going to be pissed'.

We have no idea about what they did, what's their plan... We only know that Omid likes Civil War stuff

That was the line that made me say "I like Omid. This is my new best friend". He really made me feel better after all the death in that episode.

Okay, what do we know about Carley and Doug, huh? Not much more than about Christa and Omid. Christa and Omid had also smiliar Screen time as the other pair.

I thought that Molly was their replacement

She was extremely resourceful and smart as well as being good at fighting

She was a mix of both of them as far as I was concerned

Omid brought humor to the group just like Doug. But I wouldn't say that Christa replaced Carley. Christa acted as sort of a moral compass for the group, and was smarter than Carley in general.