What can happen if you're being accused for theft by family member?

Hard to give you a reliable answer. Most police will refuse to deal with the case and say it is a civil matter because you partially repaid the family member.

He can be charged with theft and sentence to jail.

What CAN happen? Arrest, trial, conviction, jail/prison. Every crime carries potential jail or prison upon conviction. The charges actually filed by the prosecutor will determine how much time could potentially be imposed. In California, if convicted of any felony, you potentially face one or more years in prison, plus fines; on any misdemeanor, you potentially face up to 12 months in jail, plus fines. You'll learn the actual charge[s] filed and any enhancements, priors, or violations alleged, and get copies of all the police reports and prosecutors? evidence when appearing for arraignment at the first court hearing. When questioned, arrested or charged with any crime, the proper questions are, can any evidence obtained in a test, search or statement be used against you, can you be convicted, and what can you do? A little free advice if not already too late: exercise the 5th Amendment right to SHUT UP and do NOT talk to police or anyone about the case except with and through an attorney. While this isn't a 'capital case', it certainly carries potential jail, so handle it right. If you don't know how to represent yourself effectively against an experienced prosecutor intending to convict, then hire an attorney who does, who will try to get a dismissal, charge reduction, diversion, programs, or other decent outcome through motions, plea bargain, or take it to trial if appropriate. If serious about hiring counsel to help in this, and if this is in SoCal courts, feel free to contact me. I'll be happy to help fight and get the best outcome possible, using whatever defenses and sympathies there may be.