Pick 2-3 coordinating colours and 1-2 neutrals (grey, white, cream, brown).  If you have a bright colour in your scheme, keep it in small amounts with the majority of family members wearing it somewhere.  You can have many different shades of your neutrals.  Avoid very small prints on children.  Have parents wear more solid or simple patterns.  Plaid shirts look great on men.  Footwear matters; dressy shoes or boots are best.  Avoid runners.

 

A good way to choose colours is by picking a multi coloured shirt and finding coordinating clothing for the rest of the family members.  Try to start with the person who owns the least variety in their wardrobe.  

 

Buying new clothing for everyone is always best because it'll be easier to find coordinating colours by shopping at the same store.  Super Store is great with having coordinating colours in their different departments.