Gerold hightower said to jaime "you swore to guard the king, not judge him"and was sent by areys to find and bring rhaegar back. So why was he taking orders to stay with rhaegar’s bastard child and mistress? Whilst there was a massive civil war going on. Alongside with two other guards he knew were exceptional fighters.
My bet is that Aerys’ Kingsguard a) became pretty good at getting into positions where they had to take as few orders from Aerys as possible, and b) engaged in a fair amount of creative interpretation of Aerys’ orders and the chain of command if the man himself wasn’t around to look over their shoulders.
Certainly I think the fact that half the bloody Kingsguard showed up at the Tower of Joy indicates that they preferred and prioritised Rhaegar. Don’t know what they told themselves about that, because it’s super hard to imagine them thinking about the situation and concluding in all seriousness, “nah, the sixteen-year-old pseudo-hostage political appointee who’s clearly troubled by Aerys’ behaviour is completely equipped to be solely responsible for Aerys’ security in the middle of a civil war where it’s only a matter of time before his dad gets involved directly.”
