I purchased two domains they both go to the same site but i would like two sites

I’ll try and make this short.
My father-in-law contacted me to make him a website for his business, he wanted very simple, and cheap. I made him a site using wordpress.com under a premium account. He loved it, good to go!
I quickly learned wordpress.com sucks and i want to take off the training wheels. I will be transferring everything over to wrodpress.org using bluehost once the 60 day wait is up and I can transfer the domain.

Now I would like to make a site for my new photography business, I purchased a new domain name through the same wordpress.com account I have for my FIL. (stupid I know, what the hell was I thinking?)
I bought it went to my borrower typed in mynewsite.com(not the actual site) and it took me to my FIL business site.
I’m assuming these are some how linked, but I just don’t know how or why exactly.

These business’ are in no way related and I would like two different websites. So when i type in fatherinlaw.com it goes to his website, when i type in my newsite.com it goes to my website

Can somebody please explain how this works?

****I am not looking for somebody to tell me how dumb i am, or what i should have done. I need to know what I should do to move further, and fix my issue.

Thanks in advance!