Do the parents not care about Grayson abusing chase growing up?

And what ab the incest with the their omega brother

They did, Ashley used to punish Grayson whenever he hurt chase or do bad things. He used to lock him up for days in a dark room. Infact, Ashley treated Grayson the worst.

And regarding the incest things, all the Alpha brothers' (specially Chase) Pheromones were harmful to Bliss so it was Ashley who used to say them that the children will engage in incestuous acts under Pheromones control that is why Ashley sent Bliss away. Grayson don't have any words of his own. He was taught to copy and mimic from the very young age. Most of his statements comes from whatever he heard. He doesn't understand the meanings behind them

Greyson was strictly monitored by his dad because of that. And there was no incest that really happened. Their parents worried so Bliss was isolated from other siblings. Not only Bliss but their Omega Daddy Koi was also only allowed to meet the children in Alpha Ashley’s presence.