Kia will now approach Sabo to play, walking up to him when he's laying down and biting the back of his neck and trying to engage play. Sabo bites her legs, but it worries me that he is still getting in her nerves.
That sounds like Kia is getting on Sabo's nerves. He's resting and she tries to initiate 'play'.
She bites his neck, a more dominant move than him biting her legs.
Different people have different ideas on what 'play' is in dogs. I think it is not play but sizing up and establishing roles of dominance or submission in different situations.
It is natural for them to have this game and it's is healthy in the right time and place. I ask my dogs to be calm in the house and allow them play outside on walks within reason.
She isn't possessive over the humans, but will try to shove in if we are petting Sabo.
Shoving in is still not allowing Sabo have his rubs. Every one should get there rubs in peace.