Co-holders of parental responsibilities and rights must seek the assistance of ............................ when they prepare a parenting plan.

The correct option is a.

Co-holders of parental responsibilities and rights must seek the assistance of a Family Advocate, social worker, or psychologist when they prepare a parenting plan, especially if they are experiencing difficulties or disputes. This is in line with the provisions of the Children's Act 38 of 2005, Section 34(1), which specifically identifies these professionals as resources for assistance in such matters. These professionals help mediate, provide guidance on the child's best interests, and facilitate the creation of a comprehensive parenting plan.