Perhaps its worth sitting them down and trying to discuss your choice to not eat grains? Make it clear that you will not be damaging your health and are instead choosing to get your main source of fuel from fat. If you have to make a slideshow or something - there's plenty of info on this site and others to help back you up.
I understand it can be hard to get parents on board with PB, or at least understanding the choice.
Hope you can manage to get Primal with the support of the 'rents.