Moon! She, like Suns, was one of the first successful projects and were both more of test models/therapeutic companions than anything else. They were both restructured to fit their new functions but Suns has obviously undergone more significant changes... Moon is kept inside to assist with research and computational stuff. She's a lab cat. She's generally looks more like a normal creature, and has a friendly appearance because her creators (i guess it would be the ancients) would be seeing her frequently and would rather a friendly face, something that is easily perceived as nonthreatening, as opposed to Suns weaponry and NSH's extra limbs and spikes. She doesn't have the screen face like NSH, so expressing emotions comes mostly from body language. Moon is not outside at all so there is no need for solar panel components like Suns or NSH. She has internal stored power that can last for quite a while but still needs to be recharged? I imagine the neuron fly drones would also assist in that department. The drones still function somewhat like her portable processing servers/braincells. She has also programed a defensive protocol into them, they can create small bits of electricity to use in dire moments. Initially programmed to keep track of NSH's samples that sometimes escapes him.

Pebbles is a purposed organism. He is a whole entire organic cat. He was born in the lab, in a chaotic time when resources were low. He has a mark of communication. He also has a brain chip where he can access (basically) the cloud where the others upload information. He is also a lab cat so this is crucial to his role. He did try and remove it once when he was younger and it backfired horribly and now he has a mechanical ear and eye. He still feels out of place for obvious reasons, being the only creature of organic origin amongst his peers.

He is closest to Moon who had a role in caring for and raising him. She did not know a thing about caring for a living being but did her best. Pebbles does not like being confined to the facility. The suggestion and influence the brain chip has on him sometimes clashes with his thoughts. He is very aware of the limitations it puts on him to not leave. He envies NSH and Suns a lot for being able to do what he can't. He often downloads the maps they create and read NSH's sample studies in his spare time. He also likes seeing the lizards NSH brings back, from a distance.

I think in the time that Pebbles exists, NSH is not very active. Due to the low resources and chaotic season, NSH is often in low power mode. Which means less expeditions outside and more time just, half asleep. And when the weather becomes more sustainable, NSH would be sent on long outings to gather as much as possible before being powered down again. So instead of hearing stories from NSH, he sought out Suns and UI instead. (Actually I think everyone is kind of low power mode here, Suns does not wander as far).