In theory, friends and family members can do the work. The image quality is a whole different story.
There's a reason why professional wedding photography is named that. Photographers have the training and knowledge to generate excellent images regardless of the surroundings or circumstances.
Clients should ask themselves a few simple questions to clarify why they need expert help. What will family members do if there is a technical problem? How will they deal with a sudden change in weather, making clear and attractive pictures more difficult?
Amateurs are incapable of dealing with emergencies.
Furthermore, if the bride and groom have more particular requirements, they will find it impossible to carry out.