Hi Dave,
Considering the age of your girls you may look at getting a kids sail(rig) for them and a larger sail for you, but you could share a board, depending on your weight you could get a board around 130L, that both you and your girls can uphaul.
You maybe able to pick up something on this site?
Or.
Check out this link, it'll give you details of the two local stores for lessons and advice on equipment.
www.wv.org.au/index.php?option=com_content&task=section&id=13&Itemid=58Also Inverloch Windsurfing Club are holding their Learn to Windsurf series on the 8th & 9th of Jan. You can get free lessons and the guys down there will be happy to give you advice. See link for more info.
www.seabreeze.com.au/forums/Windsurfing/Victoria/IWC-hosts-the-Learn-To-Windsurf-Series-89-January/