Both parents self identify as feminists. My father has many classic blue pill traits.

Not sure what these are in this specific situation, please clarify?

To this day, my mother makes most of the decisions in the household.

Relationships where one partner is naturally more 'dominant' aren't necessarily bad, but they require that the partner with more power highly prioritise the opinions and best interests of the partner with less and have the utmost respect for them.

My father would never attempt to be dominant; I think she would laugh at him if he tried.

If he tried to be dominant, or equal? This is an important distinction. If she'd laugh at him for wanting equal say in decisions, she'd be an asshole. If she'd laugh at him for trying to dominate her, fair enough, and I'd expect that any partner of either sex would be unimpressed by their husband or wife trying to be dominant over them without their agreement.

He does not behave in any classically masculine ways, and would usually put her needs before his own.

Again, what classically masculine behaviours are you specifically referring to? Examples? Again, the partner with more power in the relationship needs to have a high level of respect for the other partner and consider their opinions and well-being: it's okay if he'd prioritise her over himself but it's likely to end up unhealthy if she wouldn't do the same.

Yet my mother would always treat him with respect. I was happy to be raised in this environment, and even today, they still make each other happy and enjoy each other’s company.

Cool. Nice to hear of a marriage still happy after so long.

My mother met him at 22, and had had previous boyfriends. Prior to meeting him she had attended college and been a leftist feminist. So very unlikely she was a virgin or had a very low N.

Is there any actual evidence that links feminism to promiscuity? The feminist women I know vary but most have had 3-5 sexual partners, some less and a couple have had a lot.