The NYS Sanitary Code (14-1) for food service establishments requires that adequate, conveniently located and properly installed (maintained and supplied) toilet and associated hand-wash facilities be provided for employee use, and that the facilities be accessible at all times. 14-1 further requires that when the facility has a seating capacity of 20 patrons or more, that bathroom facilities must be provided for patrons.
NYSDOH guidance on this issue requires separate men's & women's bathroom facilities be provided for employee use when there are 5 or more employees.
There is no restriction in 14-1 and NYSDOH guidance on this issue that dedicated employee bathroom facilities must be provided, and there is no mention of family bathrooms.
Please check with your local municipal NYS Building Code enforcement officials, as the Uniform Building Code or local laws may have requirements above and beyond those that we enforce.