Statute of limitation under Tennessee criminal law
T.C.A. 40-2-101 states that prosecution for a felony offense shall begin within:
Fifteen years for a Class A felony;
Eight years for a Class B felony;
Four years for a Class C or Class D felony; and
Two years for a Class E felony.
T.C.A. 39-14-112(c) states that extortion is a Class D felony, so prosecution must begin within four years of the date when the alleged act occurred.
Extortion is defined in T.C.A. 39-14-112 as the use of coercion upon another person with the intent to obtain property, services, any advantage or immunity. Blackmail is defined in T.C.A. 39-13-301(1) as threatening to expose or reveal the identity of another or any material, document, secret or other information that might subject a person to hatred, contempt, ridicule, loss of employment, social status or economic harm. Based on the facts you provided, extortion seems to be the more appropriate charge. It could also result in kidnapping or false imprisonment charges.
You might have better luck trying to handle the matter through family court rather than bringing criminal charges. Good luck!