I suggest you wear something you feel good in. Classic styles don't date, but that is often not an issue as you are capturing what you/your family are like at that point in time.
It is preferable to not have clothing with text, pictures or logos, as they can be too "busy" and distracting. Solid colours are great, but patterns can be fine too.
For families etc, everyone should be "coordinated" but not necessarily matching. For example, ensure that the colours you are wearing don't clash, and suit the environment you will be photographed in. If one person is in a light colour and the others are all in darker colours (or vice versa), that person will stand out and be more difficult to place in the photos.
You may wish to consider having your hair and makeup done. I am happy to arrange this for you.