Dude an incest patch takes literally 0.7 seconds to find. Patreon and Subscribestar etc. have very strict rules about incest and thus this is the only way to skirt it and allow these fine creators to make money off their hard work.
There used to be a code to unlock it, but apparently that wasn't enough, and Patreon found out and demanded the dev remove it entirely or be deplatformed. Thankfully somebody linked an unofficial patch that restored it.