No offense, but are you saying that if their DAD (who can probably sail pretty goot himself) will teach them to windsurf they won't have fun???!!
I think that that is not true, because windsurfing itself is fun. Furthermore if he will teach them, they will be having a good time together which is good for the family, RIGHT????
Peterk: I agree wit you. I think you will do fine teaching your daughters. Sooner or later, they'll become better than you and then, you will be asking them for advice. So i suggest you take your turn...
If they have the right equipment, kids learn extremely fast, no matter what kind of instructor they have (offcourse if the instructor is at least an intremediate/experienced sailor). I learnt to windsurf from my dad and I couldn't think of a better theacher if i would have to learn it all over again.
All the best and again, no offence Roger!