I would aim for really natural poses without being too posy, if you know what I mean. With just two people I would ask them to stand together and suggest daughter put her arm around mom/dad if they don't naturally do that.
I'd ask them questions about each other so that they look at each other rather than straight at the camera. Get them talking/thinking and appearing more thoughtful natural. Try posing dad on the right of your frame when he's in the shot.
I'd do a quick search of flickr for poses that you like and will appeal to the people you are photographing.
I hope this helps