Ruth had only two husbands , one was Naomis son and the second was Boaz.
Ruth's second husband was Boaz. He was a wealthy landowner who showed kindness and generosity towards Ruth and her mother-in-law Naomi. They later married, following Jewish customs.
He was the Ruth's father-in-law, and husband to Naomi.
It would be impossible to how Ruth's husband died, without knowing who Ruth's husband was. Last names help distinguish who people are, so without a last name, we don't know who Ruth is.
Tradition states that Boaz (Ruth's second husband) survived only a short time after he and Ruth were married.
Ruth came to know her first husband Mahlon in the land of Moab.
Mahlon
Naomi was Ruth mother in law, as she was Ruth's husband (Mahlon) mother
Kenneth Wakefield
She doesn't have a third husband.
Orpah and Ruth married Machlon and Kilyon, but who married whom exactly is not specified (Ruth ch.1). The order of the names, if taken respectively, implies that Ruth's first husband was Kilyon, not his brother Machlon. Her second husband was Boaz (Ruth ch.4).
Ruth's first husband was Mahlon, son of Naomi. After he died, Ruth came to Israel and married his relative, Boaz .
The bible does not tell us that Ruth had a son from Naomi son.