Why does my internet work on PC's but not on my MacBook Pro OS X 10.8.5

My two room mates and I have the same exact MacBook Pro, bought on the same day for school. My boyfriend, who also lives with us has an Acer. We also have an Xbox and a blue-ray that has Netflix on it. Everything except the MacBook Pros work fabulous on the internet. The Macs work with the wifi sometimes but only SOMETIMES. The internet company keeps telling me to connect my Mac to the modem itself to get it to work. The company doesn't understand that the new Macs don't have an ethernet port. Our internet on the laptops works literally everywhere except home which is irritating because we're in school and we NEED to have it. We need help now!! Nothing has been working. We aren't very tech savvy so we need detailed directions.