I haven't seen this movie yet, but I am quite interested. Just the trailer on the website was powerful enough. I watched it quite a few times. You kinda pick up on more and more detail as you go. The last time I watched it I noticed that the SKINNED wolf? head that they zoomed in on... blinked. I had to take a break it upset/distressed/disturbed/disgusted me so much. So horrible.
I wish wish wish people would watch this. I posted the link on my fb but I don't think anyone looked at all.
Ignorance is bliss. Blah.
Oh congrats so much on vegetarianism! Great choice.

Good on you for taking responsibility and watching the movie too. I think some things to help with your parents would be to show them you've done your research.
Maybe make a list of good veggie food so they see it isn't quite so alien, deprived and weird.
I started making my lasagnes vegetarian before I made the change, purely for health reasons and because roasted vegetable is delish.
As for health issues, you can maybe make a little fact sheet with a list of what food gives you what what nutrients. It might help them see that a diet full of multicoloured veg, nuts, wholegrains etc is really a benefit and nothing to be worried about.
Good luck.