The two grandparents, the son, and the daughter will not be contributing with a specialty dish. The relationships of those providing the specialties are as follows: The chef who makes desserts is the son's wife, so she is the daughter-in-law of the grandparents and the sister-in-law of the daughter. The barbecue expert is the daughter's husband, which makes him the son-in-law of the grandparents and the brother-in-law of the son. Therefore, the chef and the barbecue expert are both in-laws to each other through their respective marriages to the son and daughter of the grandparents.
In a family gathering, there are two grandparents, their son and daughter, and each of their children's spouses. The son has two children, while the daughter has one child. The son's wife is a chef and always makes the dessert for the family events, whereas the daughter's husband is known for his barbecuing skills. At the next family event, if it is stated that both the chef and the barbecue expert will provide their specialties, who in the family will not be contributing with a specialty dish, and what is the relationship between those providing the specialties? Respond very briefly.