If those claims are being made to the police either hire an attorney who can speak with the police and be certain they are aware of what is really going on or contact the police yourself and give them this information. Contacting them yourself is a mistake since, especially if they think you are guilty could try to trip you up or make it sound like you are just telling a story to get out of trouble. Title to the car is strong evidence that a lawyer could use to assist you.
If the family member really made out the check, the forgery allegation probably will not go far. Teh police should sed teh check to SLED for a handwriting analysis and this should confirm that the Family memeber did in fact write out the check, not you.
If the family member is pressing criminal charges through the police, you could hire an attorney now to assist you and speak on your behalf, or you could wait and see if it blows over and hire an attorney after you are charged if you do get charged.
There are a number of issues going on here so you need to hire an attorney that can guide you in the process and try to help you sought out this mess.