There’s nothing wrong with hiring a family member to be your DJ. One thing to remember is that time is money and a lot of people appreciate their time (and money).
A few pitfalls that people encounter when hiring their own family range from awkwardness at charging/paying; all the way to the DJ potentially leaving his post to celebrate with the rest of the family during the event. Don’t get me wrong, maybe that’s ok with you and as long as the DJ is experienced enough, he or she can pull it off (and as long as you’re ok with it!) but a lot of the time when the DJ gets side-tracked, the event gets side-tracked. What if your DJ isn’t experienced enough and the event becomes awkward due to it? Would that be okay for you and your guests?
Ultimately, there’s nothing wrong with hiring your family. Know the common issues with hiring family and if you have a new DJ remember that they need exposure as well so if it’s something to let them get their feet wet without too much of an impact if they mess up then let them.. At the end of the day you know that whomever you choose for your event will be exactly who you wanted.
One thing to keep in mind is that a professional DJ has a stake invested in doing a good job where a family member may end up only ‘doing a favor’ or doing something for ‘easy money’ but also understand that everyone is different so the situation you’re confronted with may be different and your family member DJ does an exemplary job.
…but, are you willing to take the chance?