What happens when you fail to send in your mortgage payment when it is due?

What if you don’t pay for the second bill they send you?

Can you still keep your house if you pay for the NEXT month’s payment?

I’m a bit worried. My mother did not pay the mortgage bill this month, because she’s going through the early stages of a divorce & normally my step dad had been the one to pay for the mortgage. He stopped paying it (only did not send in one bill) because we’d agreed to go for a short sale. However, now my mom has realized that we may be able to keep the house .. so we’re not gonna end up going through with the short sale.

I don’t wanna lose my house. ): I’m really ignorant with this sort of thing, so if someone could let me know that’d be great.