I think you understand that your weight loss disproves their comfortable lie that it’s all genetics and they can’t help it. That’s why they’re trying to sabotage you.
My advice is to keep quiet. Your words will not convince them to change, although your example might.
And when they mention your body type, again, shut that down. Let it be known that all talk of weight, body type, diet, or exercise is off the table when you’re around, and walk out if they won’t stop. They’ll soon learn you’re serious.
Misery loves company. You’ve already proven you can do it. Keep it up.
Well done you! They are afraid, you are now different because you’re no longer like them. Get them to watch 1000lb sisters or any of the programmes that are similar. I think you’re awesome, you’ve got your weight down to a healthy BMI and perhaps eradicated a whole host of future health issues. Keep it up!