The only thing I can say is do your research, and present it to them in a thoughtful manner. I do have a few questions for you though, you say your dad gave you the "wrong image" talk what does he think that image is? Also I was wondering if it is a cultural thing, did your parents grow up with kilts around, if not this may be an uphill battle for you.

I think it would be a great idea to take them to a Burns Dinner or any other function where there will be kilts, I know its a few months away but Tartan day is in April, here is the link to the website

http://www.tartanday.org/

I think positive images, and articles may help sway them, just keep communications open with them and sooner or later they might just come around to your way of seeing things.

Good luck and keep us posted.