Since I already read the novel, maybe this will help
@Eitu
YW pheromones actually affecting Keith. Keith told YW to control his pheromones because Keith want to shame YW that trying to make Keith control his own pheromones. It's like "I'll control mine if you control yours."
But you could see (in this chapter) that Keith is disappointed because he couldn't smell YW pheromones.
As for Keith, he has a high pheromones level because he is a dominant alpha.
Also for insemination with many partner: He is a dominant alpha, so he could control his semen if they could impregnate the partner or not. Except if he was in the condition that he can't control himself (like in a worse or very bad rut). I think this already explained in the early chapters.