3 ways that help me stick to my decision to be healthy when my family is not onboard.

So you jumped on the diet train but your family just can't kick the junk food.  I feel you.  My husband is the worst when it comes to this, he is always trying to tempt me with some kind of treat.  This is where you have to be firm and really practice self control.
First thing to do is tell your family about your decision to get healthy hopefully they will want to join.  If they are reluctant to join hopefully being a good role model will change there mind.  After all its much easier to stick to your goals when you have a great support system in place.  I'm still working on my family :)

Second meal planning is so important, if you plan out what you are going to eat and at what time you are going to eat it, you are more likely to stick to your diet.  This works wonders for me it takes the guess work out of figuring out what to eat.  For me following a low carb diet, I just have to tweak my dinners a bit to make it work with my family.  For example say I make tacos, my family eats there taco in a taco shell and I eat mine as a salad or in a lettuce wrap.  It can be challenging at times but I know what my goals are and the healthy swaps taste just as good, you just have to be in the right mind set.
Third exercise, when you put in the time to workout and see how hard and how long you had to work to burn those extra calories it makes you think twice about sabotaging your diet with tempting treats.  Exercise can be fun and even if your family doesn't want to participate in your healthy eating habits, maybe they will partake in a family walk and its a great way to spend time together.