preemie, what you are describing here is something many people with families go through. you want to make healthy changes in your life, but battling poor food choices with your husband and kids can be really hard, but not impossible.
firstly, to address your motivation problem for exercise. make yourself a workout schedule and stick to it. going to the gym is good, but also mix it up a bit to keep it interesting. i also recommend group workouts like aerobics, spinning classes and step classes if your gym offers it. also, a physical activity planned once a week for the whole family, like frisbee or soccer in the park or a family bike ride will get your other family members involved too.
secondly, have a sit down with your husband and put your heads together about how you and your family can eat better. these diet changes you wish for aren't just about making you healthier, it should be about making your whole family healthier. i find that making a meal plan for the whole week is critical. on sunday i make a list of the meals (breakfast, lunch and dinner) that i will be eating over the next week. i then buy the groceries for these meals and do as much prep ahead of time. if you aren't sure where to start, buy yourself a low-fat cookbook that has really simple recipes and use that to become inspired. some meals i make during the week are so simple that it would take me longer to drive to mcdonald's and buy fast-food than it would to make a healthy meal. i would be happy to pass along a few of my favorite recipes if you like.
Happy Canada Day by the way! Whoo hoo!