Okay, so timeline-wise, I was thinking that could go something like this:

- Drei talks to Zalla again either at the end of this day or the beginning of the next one, and she tells him that their fertility specialists want him to bring Artemis on board the ship, so they can speak with/study her.
- He takes her up to the ship, and that's where all the stuff goes down that we talked about before
- Since Artemis can't live off the same food that the aliens eat, they would have to go back down to the earth after it's decided that they're going to be a breeding pair.
- Drei would be taken off the team that was originally assigned to clear out the rest of the humans, since his leaders would find it more important for him to be part of their experiment. However, he and Artemis could still explore the area, and that's how they end up running into those different groups of humans that you listed out earlier.
- All the while, they would be sleeping together intermittently to find out if their two races really can breed, which would cause some awkwardness while they have yet to confess to each other that neither of them are doing it just because they were told to by the Om'phaers

That should give us some direction as we navigate the next parts of the story :) What do you think?