Having a family member who is both good at something that can help you and willing to use their skills for your benefit is not the most common combination, and it is something to be treated with respect. Just because somebody is related to you doesn't mean that they are obliged to share such a gift, and it could well be something that people pay a lot of money for otherwise.
Of course, the thing about receiving familial help is that the drama of being related to one another often gets in the way. The exchange gets turned into some kind of weird power trip complete with all the complications that almost always come with family relationships. When you consider it this way, it isn't really any surprise that relatives who have a service to offer aren't always happy to do it for those who they should be closest to. It becomes more of a headache than it is worth, especially if they are doing it for free. There is a reason a lot of people do not want to work with their family members.