I've found low carb is great for willpower, because there are so many naughty things you can have. If I make a roast and do creamed leeks, buttery garlic carrots, and a cheeseboard for after, the only thing I can't really have are the potatoes, so I don't get that 'not joining in' feeling.
I find being able to eat pate, cured meats, cheese and smoked salmon stops me feeling totally Puritan and miserable when everyone else is tucking in.
Other tips from me would be exercising. Even a little bit of exercise tends to stop me feeling like eating unhealthy food, and I just sit there with an apple (if not low carbing >.>) feeling smug.
Cadbury Hi-Lites hot chocolate is quite low cal, and I find that can be good in the evenings if people are snacking on chocolate/biscuits as it takes the edge off (again, not if low carbing). Or Hartley's no added sugar jelly.
Ultimately, I think you have to find what's right for you. Some of my friends like the total control of a Lighter Life style meal-replacement plan diet, because there's no room to start sliding, but I have too much of an emotional relationship with food for that. I need to feel like I'm enjoying what I'm eating. So, for me, it's about a diet that includes foods I love, so I feel like I'm treating myself. It sounds food is a really social activity for you and your family, so maybe you need to get them on board a bit, and start trying to make healthy/low calorie treats that you can all eat together?
As for meals out with friends etc, two rules: never get drunk (alcohol murders willpower), and decide what you're going to have in advance. If you go in and say, 'God, I LOVE the steak salad here' you're way less likely to get the whole 'oh, come on, you're being too hard on yourself! Have a pizza with the rest of us' shtick that you get if you go in saying, sadly, 'I'm on a diet, so I'm just going to have the salad'.