That's definitely Jon's next step :) The only reason he didn't do it before is that at that point, they still wanted to have more kids eventually.

From the beginning this fic was supposed to be OTT about the babies, but even with that, yeah, four seems like the place to stop. And don't worry, Stephen will keep his career, no trouble. They're both millionaires; they can afford to hire plenty of childcare.

Yes, Stephen's genitals here are small because he's an omega man. The rest is personal preference, though: this Stephen is just one of those guys who doesn't care much for receiving oral, same as sometimes happens IRL.