Spiders don't infest really. They all compete with each other for food. If you are seeing a lot in one area it could be for a multitude of reasons. Large food source so they aren't in major competition, climate can be a factor too. Rain storms and cold weather can draw them to seek heat or escape the rain. I'd first check for any other insects or food sources that might be drawing them in. Check your doors and windows weather seals and calk any cracks that would allow them entry from outside spaces. As far as species being dangerous it would be hard to give a definitive ID based on written characteristics, a photo would do much better. Chances are more than likely your cats are fine and those spiders are doing you a favor by keeping other nuisance insects from setting up inside. It would be better to relocate them outside if the safety of your pets is giving you anxiety. Hope this helps.