incest is easy to turn on, but any other sex is turned off, the event triggers are somehow cleverly written, or I'm just so stupid and don't notice something in the code!
Incest plus every sex is turned on in my patch (minus sex with minors, of course).
Also, you're not stupid. I got confused at first too. For the sex acts, setting mychild and incestblock to true would make it so that only incestuous sex is possible. No sex with slaves, servants, or even your wife.
And keeping it on "isnot true" would not make incestuous situations possible at all.
So what's the solution? Delete them from the code. Instead of modifying them to "is true" or whatever, just remove them; ideally removing the "$cens" variable as well, since that could complicate things due to it having both a "1" and an "undefined" aspect associated with two different areas pertaining to incest.
Be careful with removing certain "$cens" though. Not every one should go—you'd break incest, maybe the game too. I can tell you're already capable of handling the code, so just read, analyze, and see what's what.
Edit: Actually, I double checked and think I'm remembering incorrectly (messed with too many lines of code, my b). It isn't necessary to touch the "$cens" variable at all. It'd actually be best to leave it alone. Don't remove it anywhere. Don't change it all.
Do go ahead and delete the mychild and incestblock wherever necessary though.