You have to do this for YOU. Not because it's not fair to your husband, but because you WANT to. It's so easy to procrastinate, and when you look at a goal that seems insurmountable, inertia sets in. There's an old question: "How do you eat an elephant?" The answer is "One bite at a time." It might be better for you to not look at 40 pounds or a gala in March.
I think it's more telling that you "don't enjoy eating healthy" - that may be because you have always rewarded yourself with salty or sugary or convenience foods, or because you were raised that way. (I was and it's an eternal curse!) There's also a perception that you have, that "healthy eating" is tasteless and boring, endless rabbit food and based on deprivation, because the "good stuff" is fat and white flour and sugar.
Looking at a treadmill or a workout tape and getting motivated for a solitary stint on the equipment is easy to postpone especially with a full lifestyle - 6 kids is a handful, and there's always something "more important" to do like laundry or food shopping or working to integrate a blended family of kids who come and go. That's a lot of stress!
Now, let's look at the 6 pounds in 8 days. You didn't lose that weight. You deprived yourself somehow and lost mostly water weight. That's why it came back so quickly. It wasn't real, so forget about it. If it WAS real, it wasn't healthy! So you deprived yourself, and your body went into starvation mode, and started storing calories as fat. It's an evolutionary and primal response to food deprivation. So you have to get past it.
You all have to agree as a family about how you are going to eat and what you are going to buy. I realize it's hard with a yours/mine/ours set up and 5 out of 6 kids who spend at least part of their time with another parent. You are probably trying to please everyone as well as not spend your life in the kitchen as a short order cook. So you go for what's popular, easy, tasty and palatable for everyone.
You really are setting yourself up for disappointment, but you are also setting up 6 children for a lifetime of frustration because they, as adults, will fight the weight and the food choices they make now. I think the solution has to be making food a family affair - finding new foods to eat and experiment with, making cooking a joint project that everyone has a part in, and making it all FUN and not deprivation. Making a family salad bar can be a lot of fun, and you can get kids to try new things if they can a) choose them b) prepare them c) dip them in something like hummus. Making a taco bar lets you choose a little bit of "bad" food and mix it with healthy add-ins. There are all kinds of magazines and cookbooks that make simple and healthy additions - try Rachael Ray (how to cook a week's worth of meals with just a few ingredients mixed in different ways) or J. Seinfeld (how to sneak food into kid-friendly recipes that are FUN. Have everyone pick a recipe and then everyone gets to try it.
You can also make some easy substitutions that will keep you all more satisfied. For example, sweet potatoes cut in spears and oven-fried on a baking sheet with a little olive oil are much better than French fries. A nice lean meat turkey burger (or half grass-fed beef and half turkey) with added vegetables for moisture (we use frozen spinach, chopped onions, some horseradish, refried or other mashed beans) and put it on a whole wheat bun with a slice of tomato and some lettuce - it's filling. We make our own chicken nuggets with wheat germ and Parm cheese, sometimes with ground up almonds mixed in, quick fried in the skillet with olive oil just to crisp up the outside, and then finished in the oven. We grill all kinds of vegetables including broccoli, green beans, asparagus, corn, beets, kohlrabi, and zucchini. I make lasagna with whole wheat noodles, a mix of cottage cheese and tofu instead of ricotta (mix in the seasonings and no one can tell), and I even puree some cooked eggplant or mushrooms in the sauce. We make stir fry for healthy Chinese food. Kids like to sort the veggies by cooking times, and they can choose chicken or beef or tofu. If you want any recipes, let me know. And you'd be shocked at how much good stuff you can put in an enchilada - great refrigerator "clean out" recipe, with some brown rice made with a little tomato puree instead of all water.
The other thing might be to join a gym with a class of women like you. I have a phenomenal class that I joined when the instructor stopped by my treadmill and invited me in. We do a lot of weight training which is good for the muscles as well as the prevention of osteoporosis. We encourage each other, laugh, sing along with the music...and we have pot luck dinners every couple of months (we call ourselves Women, Weights and Wine and similar cute names!). So if you make exercise a fun, social event, either with other adults or the family or both, it won't be punishment that you force yourself to do and hate. I also take a book to the treadmill at the gym and get lost in what I'm reading - the book covers the timer, and I have a special clamp that holds the pages open. I'm shocked with how much I do without feeling pushed. And it's 30 or 45 minutes with no one asking me for juice or to referee a fight.
You may also be nourishing yourself insufficiently - so comprehensive supplementation is really important to meet your true nutritional needs and keep you from craving the stuff in the cabinets that is just empty calories. I've had extraordinary results, and have fewer health problems, less medication, and phenomenal lab results. Believe me, you don't want to weight until your doctor says your cholesterol is 260 and your blood pressure is 160/90 and you need medication. Don't do conventional grocery store or health food vitamin pills - very low absorption, waste of money, insufficient nutrients. I can help you more in this area - I've found much more stamina and energy for working out without being hungry or lightheaded, and without any injuries. If you're not an exercise fiend, any ache or pain is enough to sideline you.
You can substitute some healthier snacks - almonds have more protein and will hold you longer than pretzels, but they still give you the chance to crunch. Don't get hungry - that's the key. Eat 3 meals and 2 snacks for sure.
Drink more water - a lot of "hunger" is really thirst. And it's filling, and it helps process the rest of the meal.
There's a simple zucchini crisp snack that's yummy: zucchini disks dipped in a little olive oil and then dipped in a mix of Parmesan cheese (which is already salty) and panko bread crumbs. Sprinkle extra crumbs mixture on top. Bake about 15 minutes at 350 or so until the crumbs are browning. Way better than chips -- and I'm a serious chip lover.
I think you are also dealing with some stress - you say you have some stressors but basically everything is fine. My guess is, you are making everyone else's life fine, and sacrificing yourself. Stress also produces hormones that lead to fatigue and brain fog - so some mental clarity and healthy energy might help. There is new science in this area. Do not get into caffeine or other stimulants, but there is a nutrition-based product you can use for more focus. But I think your lifestyle can be overwhelming - I am a stepmother and a mother, so I know a little about the scheduling and the integrating of different families into one - and it's a lot for anyone to take on!
So I think this is a multi-faceted issue and one you are trying to do all by yourself - and then beating up on yourself when it doesn't work. So many of us have been there and we do understand. But there is help available!