This is one of the biggest questions I get as a photographer. What should we wear??
First I recommend that you wear something that is comfortable in and is within your normal aesthetic. It helps when clothing feels great to wear, instead of focusing on some discomfort, it is easier to get relax into the photos.
Secondly I would advise you to stay away from logos, neon colours or too many patterns. This doesn't mean everyone has to wear black, but when there are competing graphics and patterns, our eyes are drawn away from the faces of the people in the photograph to what they are wearing.
Third consider how the fabrics drape and move. Sometimes thinner materials show what is underneath and create lines and creases. Be aware of how the clothing you are wearing looks while you are sitting or if button up shirts gape.
Fourth is to coordinate instead of match. Think about complimentary colours that can work together. Pinterest is a great option for this with a lot of colour schemes to suit your family.
A small side note: Hats, sunglasses, hoodies can cast shadows that make it difficult to see your eyes. That isn't to say that you can't wear them, just be aware of how affect the photos.
In all of this what is most important is to pick clothes that boost your confidence and are comfortable to wear.
As always with any questions for your specific photo shoot, please don't hesitate