I got used to the Spivak after a while, and while it'd be optimal for an audience used to it, it did detract a little at first. On the whole I'd say it's necessary though (if you were going to use a gender'd pronoun, I'd use female ones)

I read Key as mainly female, and Trellis as more male- it would be interesting to know how readers' perceptions correlated with their own gender.

The children seemed a little mature, but I thought they'd had a lot better education, or genetic enhancement or something. I think spending a few more sentences on the important events would be good though- otherwise one can simply miss them.

I think you were right to just hint at the backstory- guessing is always fun, and my impression of the world was very similar to that which you gave in one of the comments.