You do not need to try to make it work with someone who thinks of people as “illegals.” Just divorce them. Those divorced couples made the right choice.
This may not always be possible. Some people may not have the financial or practical means available to get a divorce, but if you do have those means? DIVORCE THEM.
Because if one member of a couple believes the President should endorse police brutality and the other member believes that is balls-to-the-wall insane, that is not a disagreement you’re going to find common ground on. You can use all the measured voices and positive words you want. It’s not a question of disagreement about the most effective way to load the dishwasher, or even whether trickle-down economics works. Those are opinions that might be altered by showing compelling factual evidence.