Preventing spiders in the basement

Lots of reddit just says "they're there because they're eating other insects." That's great and all, sure. My wife has an extreme fear of them, however, and has injured herself multiple times because when she sees one, she jumps into the nearest hard object and hurts herself. I'm looking for a way to spiderproof my house. My parents' house growing up did not have spider issues, and they also were not overrun with other insects. Same with my grandparents' house, and many other homes I've gone into. Our house has these great big (relatively) spiders, maybe 1 to 1 1/2 inches in diameter that just pop up at random. I cannot figure out where they come from, and I kill about 3-5 a day every single summer. They go away from October to March every year, but always come back in the summer. They like to hang out in our downstairs bathroom primarily, though they spend a lot of time where our TV is too, on the couches, climbing into the basket that has our blankets, etc.

At this point, I'm tempted to set up a security camera and just watch where they are coming from, because I cannot figure it out. How do you find out where they're coming from? How do you prevent them from getting in all over the place?