I once let two cousins become romantically involved even (I could because I had moved my sims to another world/new save so they didn’t recognize each other as relatives anymore). Actually, in real life in most countries cousins can actually marry. The ‘ew’ is between our ears, technically there’s not much wrong with it. Other than a slightly bigger chance of getting children who can’t reproduce (a risk comparable to a 35+ woman who gets pregnant for the first time, which we don’t consider ew either). Charles Darwin married his cousin I learned (when I did all this research because of my storyline, which in fact was mainly based on the fact that I liked to mix their genetic features). And as for further back: my own real life parents alledgedly share the same ancestors, a few generations back. There is no biological reason why that would be unadvisable.
