You have to speak their language. And by "speaking their language", I mean hitting them with clubs and dragging them to your base like a neanderthal. Then you domesticate them like animals - put them in cages with food and wait for them to become obedient, then deploy by right-clicking them. Finally, increase you relationship by adventuring together or by dancing together with Q. You need at least 50 relationship to have sex without rape.
Unique characters have more complex requirements, usually depending on the dialogue choices. I recommend checking John's guide.
Mine stations are just inefficient at getting iron. Doesn't matter what you do to them.
Up to 3 workers can work the mine at the same time, and it seems that their stats or type matter, while the biome does not. But it does not change the final result of mines being much, much worse than just going into a mine and mining some iron yourself.
Also, if you put a mine really far north, it will produce diamonds in addition to stone and iron. But at that point, you are unlikely to need diamonds anymore.
You can disable "love" in their status settings, and they'll stop having relationship trouble. But for best results, you should arrange for compatible people to live together.
As others have said, if their moral is low, they will take breaks for rioting, and this will decrease productivity.