Second and third cousins can legally marry in most places IRL. It might make for awkward family gatherings in the west, but it wouldn't raise an eyebrow in some places. Even first cousins are considered ideal marriage partners in more than a few non-western cultures. Our cultural preferences are not the norm globally or historically.
Given the sheer number of bugs surrounding relationship status that have finally been fixed, I can't fully support further complicating the code. Sims aren't real people. They are a few lines of code and a series of animations. Please don't break the game in order to track distant relationships. If it can be done without messing things up, I'm more open to it. I still think tracking distant cousins is too far, though. If real people can marry them in California, imaginary characters should be allowed to marry them in a make-believe games.
Issues with mods need to be addressed with the creators of the mods. The game allows, but doesn't officially support mods. Accounting for mod behavior is more than any programmer should be asked to do. The official game code is complex enough. I use and enjoy MCCC, but it will do some wonky things with relationships. Not the game's fault, and there is nothing they can, or should, do about it. If you use mods, you assume the risks.
