This probably isn't what you want to hear, but I've given up on trying to get my mother and sister to live healthier livestyles.
My mother is 4'10" and weighs over 165 lbs, my sister is 5' even and weighs over 170. They both have little to no activity all day/every day, and fast food makes up the majority of their meals.
At the same time, I hear them talk about not giving my sister's kids too much protein, and when I ask my nephew if he wants to try some of my protein shake I get replys like "Don't give him that stuff..." The poor kid has a small appetite as it is due to a herniated diaphragm when he was born, and he's in the 2 percentile for his weight.
Anyway, don't give up right away. I did get my wife to workout with me and eat much better (she's doing CW's ABBH I right now
She said that watching me go to the gym all the time made her want to do it too. Plus, my family sees me much differently than my wife does. I'm still the youngest who doesn't know anything in their eyes.