I think its a lot simpler than you think. If you disable "same sex try for baby", and then try to have a baby with two sims of the same sex... that's extremely likely why its not working.
You DO know, you can disable random pregnancies in MCCC's story progression, right? You can disable everything in story progression if you want...
No random pregnancies:
Go into "MC Pregnancy/Pregnant Sim Selection/Pregnancy Percentage" and set all age groups to "0"
No random marriages:
Go into "MC Pregnancy/Marriage Sim Selection/Marriage Percentage" and set all age groups to "0"
If you don't want ANY babies showing up at all... (except yours) you'll have to disable them in MC Population also so none are created automatically to fill houses... "MC Population/Populating Settings/Percent Baby"
Don't want sims to randomly break up?
"MCCC settings/Relationship Settings/Breakup Settings" and set both Couple and Spouse "Relationship change percent" to "0"
It'll do what you want. You just have to find the right settings. And there are a LOT of settings...
