Laire is still in the Threshold but she's super cute and lovely, really clingy. Really chatty. A bit of a princess. So she could easily fit in with either of them- it'd be funny to see her with the filly because she'd cry if Bathsheba said anything remotely upsetting. She could also be like a friend or love interest to Aurum, and would definitely try and make him social. She doesn't understand how people can be alone.
Nero is like the opposite and is a total outcast douchebag who was a kind soul underneath it. I think Nero and Aurum could be friends if Aurum could get past his super prickly exterior at first. They could definitely teach each other a lot. Nero loves foals so totally wouldn't be mean at all to Bathsheeba but idk what else there would be for them.