GH Weight-Loss Support Group

This past weekend has to be one of the worst of my life, so far. My mother and father -in-law visited. They live out of state and don't often make the trip. We, usually, see them once a year.
Some background info: I'm 35. My husband is 52. We have 2 young children. Our son is 3, our daughter 18 months. We've been married for 5 years. My husband and I have each been
overweight for a long time. I'm 5'2" 290lbs. My husband is about 5'8" 245lbs. I've always been heavy, even as a child. My husband only gained a lot of weight after he hit 40 and was put on a medication for an ulcer.
My in laws are in their late 70s. They used to be heavy set, too. My mother-in-law used to weigh over 200lbs and my father in law was about 270lbs. A couple of years ago, they started this diet called the Atkin's diet. They lost a lot of weight. 80lbs for my father in law and over 50lbs for my mother-in-law, in the first year. They have lost more than that, now.
After they had tried it for awhile, they bought us the diet book and cookbook as a gift,
and suggested that my husband and I try it. We tried it for awhile. My husband lost about 30lbs. I didn't lose any and in fact, gained about 25lbs. During the diet, our grocery bill nearly tripled because meat and cheese (the low carb diet mainstays) are very expensive here. Financially, we couldn't afford to continue that for long. (Which we explained to my in laws, last year.)
This past weekend's visit was supposed to be about celebrating my 35th birthday. Only it wasn't a celebration, more like a roast. My gift from my in laws was what they
refered to as an incentive to lose weight. A cute designer outfit (low cut top and hip hugger capris in a style only very thin women can wear ) in a size quite a bit smaller
than I wear, now. I wear a 30W. The outfit is a misses size 14. My mother in law removed the tags, so I wouldn't return it.
Then, my mother-in-law had to criticise my cooking. (I had take exceptional care in preparing the meal and making sure it fit in with the Atkins way of eating by following a recipe in the cookbook. So, I felt really hurt by those comments, as well. )

Instead of defending me, my husband joined his parents and made matters worse by insisting that it was all my fault that he didn't continue with the Atkin's thing,
that I never do anything around the house like cleaning, etc. (which is simply not true.)

After crying for a long time this morning, I have decided to try to lose an astonishing amount of wieght or die trying, just to shut them all up. I have no idea how to achieve this. A healthy weight most doctors recommend for me is 125lbs. I, now, weigh 290lbs.
I have to take a lot of medication due to medical problems. Coumadin, most notably, because I have a genetic blood clotting disorder.
Because of that medication, I can't dramaticly alter how I eat or what I eat without messing up my PT and INR levels.
Also, because of that any injury could lead to substantial dangerous bleeding and extensive bruising, so exercise isn't really a good idea.
I also have knee and back problems and carpel tunnel syndrome, and asthma.
My doctor said he is skeptical about any diet or exercise program given my condition,
but that the decision rests with me.
I'd like to try the Atkins thing, again. Eventhough I gained weight the first time, as my mother-in-law insists everyone can lose weight on it if they stay on it long enough.
Does anyone have any tips for making the Atkin's diet work?
Also, how do you manage to do Atkin's on a limited grocery budget?