The Patriot

During the American Revolution in 1776, Benjamin Martin, a veteran of the French and Indian War and a widower with seven children, is called to Charleston to vote in the South Carolina General Assembly on a levy supporting the Continental Army. Fearing war against Great Britain, Benjamin abstains; the vote is nonetheless passed and, against his father's wishes, Benjamin's eldest son Gabriel joins the Continental Army.
Four years later Charleston falls to the British and a wounded Gabriel returns home carrying dispatches. The Martins care for both British and American wounded from a nearby battle, before British Dragoons, led by the ruthless Colonel William Tavington, arrive, arrest Gabriel, and take captive the African American free men and women who work Benjamin's land. When Benjamin's second son Thomas tries to free Gabriel, he is shot and killed by Tavington, who then orders the Martins' house burned, and wounded Americans executed. After the British leave, Benjamin gives his next two eldest sons muskets, and they ambush the British unit escorting a tied Gabriel. Benjamin skillfully, yet brutally, kills many soldiers with his tomahawk. A British survivor tells Tavington of the attack, earning Benjamin the moniker of the "Ghost". Benjamin and Gabriel resolve to fight the British, leaving the younger children in the care of Benjamin's sister-in-law, Charlotte. On their way to the Continental Army's camp, they witness the southern Continental Army under General Horatio Gates engaging the British Army. Benjamin recognizes the foolishness of the action; sure enough, the Continentals are decisively routed.
Benjamin meets his former commanding officer, Colonel Harry Burwell, who makes him colonel of the local colonial militia due to his combat experience. Benjamin is tasked with keeping Lord Cornwallis's regiments pinned south through guerrilla warfare. French Major Jean Villeneuve helps train the militia and promises more French aid. Gabriel asks why Villeneuve and others mention Benjamin's role in something called "Fort Wilderness". Benjamin says that when he was fighting in the royal British army in the French and Indian war he and several other soldiers were sent on a mission to assault a French fort called "Fort Wilderness" where he and his comrades literally cut the defending French soldiers apart slowly, revealing why Benjamin is always hesitant when asked about the event and why he is haunted by his past. Benjamin's militia harass British supply lines, even capturing some of Cornwallis' personal effects and his two Great Danes, and burn half the bridges and ferries leading to Charleston. Lord Cornwallis blames Tavington for creating this reaction with his brutal tactics. However, irritated at the lack of progress, and insulted by Benjamin's clever ploy to free some of the captured militia, Cornwallis reluctantly allows Tavington to stop Benjamin by any means necessary.
With the reluctant aid of the Loyalist Captain Wilkins, Tavington learns the identities of some militia members and proceeds to attack their families and burn their homes. Benjamin's family flees Charlotte's plantation as it is burned to live in a Gullah settlement with former black slaves. There, Gabriel marries his betrothed Anne. Tavington's brigade rides into the town that supplies the militia. He assembles all the townspeople, including Anne, into the church promising freedom in exchange for the whereabouts of the rebels. However, after the location is given the doors are barricaded, trapping the people as Tavington orders the church burned. After discovering the tragedy, Gabriel races to attack Tavington's encampment. In the ensuing fight, Tavington mortally wounds Gabriel before fleeing. Benjamin arrives soon after, only to have another of his sons die in his arms.
Benjamin mourns and wavers in his commitment to continue fighting, but is resolved when reminded of his son's dedication to the cause by finding an American flag he repaired personally. Martin's militia, along with a larger Continental Army regiment, confronts Cornwallis' regiment in a decisive battle at the Battle of Cowpens. The British appear to have the upper hand until Benjamin rallies the troops forward against their lines and Tavington rushes to personally target him. The two duel and Tavington gains the upper hand, delivering several wounds to Benjamin. A beaten Benjamin slumps to his knees, and Tavington prepares to deliver the coup de grÃ¢ce. At the last second, however, Benjamin dodges the attack and stabs Tavington to death, avenging his sons' deaths. The battle is a Continental victory and Cornwallis is forced to retreat.
After many eventual retreats, Cornwallis is besieged at Yorktown, Virginia where he surrenders to the surrounding Continental Army and the long-awaited French naval force. After the conflict ends, Benjamin returns with his family and discovers his militia men rebuilding his homestead in their new nation.

Question: Who is Benjamin's sister in law ?
Answer: Charlotte is the sister in law of Benjamin.