I am trying to determine what amount of individual taxes are associated with the ownership of a rental property?

I took over ownership of my parents property 7 years ago (they now rent from me). The only other property I own is my personal home which is 15 years old. Last year I found myself owing a considerable amount ~ this year it is double what I owed last year. I have a sibling who is willing to help with this added burden and I'm trying to figure out how to calculate what portion of this tax debt is associated with the 2nd property ownership.

Thank you in advance for your help.