Consider: Timeline where the twins have been with overwatch for about a year at the least. While still wary, Blue's more chatty and friendlier, though Red still initiates most things between them and the group. They're assigned out on a particularly dangerous mission, and things go south. No one knows all of what happened, but one thing is certain. The twins didn't make it out. The process of 'cleaning' out their rooms and areas takes a while, but fully comes to a halt once one of the notebooks is found.
The lifetimes the twins had lived weren't overly talked about, but they weren't a secret. Red chatted with Winston sometimes about the "Respawn Circumstances" as D.Va jokingly called it, and the theory they all agreed was most likely was coming up. With the eyes they have everywhere, Overwatch puts some focus into attempting to see if the twins had been reborn, and several areas are marked as likely to have them there, based on fuzzy sightings and local rumours.
But everyone's uncertain about one thing.
How?
Will they be babies? Will they be "cubs" as Blue described it? Will they remember Overwatch, or will they run and hide from their former teammates? What if Talon gets a hold of them? Should the group try and find them, give them a "good childhood" as Red had described, not that it would be hard. Food, a warm place to sleep, a bath or a shower, and the little ones would be easily willing to do anything. Blue had admitted that he'd done things in order to get those, and he doubted it would be the last time.
Would they even trust Overwatch, especially if they seemed to be offering this all for free?