Let me say that you typically can treat the LLC as a pass through entity regardless of whether or not you have 1 or 2 members. You will have to go from using the schedule C to the schedule K if you add your wife. Each year your LLC should file the same tax forms as a partnership, meaning you would file a Schedule K. Your LLC would also prepare a K-1 form for each of the members (in this case you and your spouse).

The LLC is still considered a non-entity but is merely taxed as a partnership (when there are 2 or more members) or taxed as a sole proprietor if there is only 1 member.