You add people to the title of a house by having a new deed prepared adding them to the part that says "grantee".  All the titled owners have to sign the new deed under "grantor".  You are best to speak with an attorney about doing this and which deed is best under your situation.  There are "better" deeds for title that quit claim.  As for the cost, there are also filing fees set by the county clerk.  Good luck.