I'm so sorry you had to deal with this in-law and even more sorry that you felt like your husband did not come down on your side. That is a horrible feeling, and difficult to overcome. But you picked yourself up and decided that you are going to come out of this a winner, and that is great!
Emotional eating is our enemy - we get upset or depressed over something, and then compound it by hurting ourselves with food. It doesn't really make any more sense than poking ourselves with a fork because we are upset with the world. Poking ourselves with forks would hurt less in the long run, but for some reason we don't poke ourselves with forks - and we do overeat.
Breaking that pattern is a HUGE step, and something you should be very proud of. And remember, you can do a lot of things to alter your body, but what really matters is the person you are on the inside, and you are a loving, honest, caring person. That puts you miles ahead of your brother-in-law, and it is something he does not even have the capacity to understand.