Is 80 GB of home internet enough?

So I have 80 GB of home internet at home. There's one computer, and a laptop. My cousin uses his Ipod and i use my Iphone for internet. We ALWAYS get bills of over 200$ per month which is not our plan. I use a lot of Instagram, Vine, Twitter and Facebook and i rarely facetime but when I do I use it for about an hour. That should'nt take that much space does it? I watch a couple of videos too but not that much. My mom only uses the internet to check her bank account but other than that there's my cousin who also uses the computer and sneaks out at night to go on It. He's always playing games and other stuff that we don't know. But on MY side am I using a lot of internet…

From all that you listed it won't take long to use 80gb of bandwidth. Also do you have your router security set up. Anyone in range of your router can connect on it if it is not set up with a secure password to connect to the router.