Is it normal i don't understand this?

I just accidentally stumbled across a check of my mother's and immediately was shocked when I saw her yearly income of just 25,000 a year (we live in NY and it's expensive).

My Father I know usually makes $40,000 and 45k on a good year.

Combined, their income would be 65,000 but that makes no sense because the house we live in right now is completely paid for as my parents celebrated the 15 year mark a few years ago of having completed paid off the mortgage of the house. This house was $400,000 when we moved in. How could they have afforded this house, my college/my brother's college on just 65k a year. My college was cheap but combined, my brother and i spent about 25k. How is it possible that they were paying for the house, our college and more stuff like phone bills, special tv subscriptions, new appliances all the time, etc?

My mother used to tell me she earned the same as my father but when I saw 25k, I knew she must've been lying unless, is it possible something was deducted and not shown? I doubt that.

is it normal they can afford this on nothing?