Okay I don't know much about these terms so sorry but this is the situation.

My mother bought a house a while back and she put herself and my sister as the buyers. My sister at the time was married, but her husband told her to sign as single, and she did (we knew nothing about buying houses). Now my mother has sold the house, and my sister is fine with that and does'nt want any money. But her husband says that a part of this money belongs to him and he want to divorce my sister in order to get my mothers money from the house. My mother plans on using the money for a new house that she and my sister and her two girls will move into. Does he actually have a right to the money? even if my sister doesn't want the money?

Your sister misstating her marital status when buying was not a problem, not an issue, although she probably violated FEDERAL law, lying on mortgage applications.
However, her husband may have a claim to an interest in the house, and the right to tie it up in court, as they were married during the purchase. She can probably defeat his claim, but it will take time and money. He needs to sign away his marital right in home.