OP NRTFT but wanted to offer my understanding.
My children attended a primary school where there were lots of slim 'Boden moms'.
My children had previously been at nursery in a different area, so it was a bit of a contrast when they moved schools and we found ourselves mixing with more 'middle class' families.
Unsurprisingly, recent data showed that the poorest parts of my home city had higher rates of child obesity than the most affluent areas - my DC's school sat in one of those the affluent areas.
After having my twins I gained a lot of weight then lost it - but it took 2 years. It was a tough time for me body wise, so I understand your feelings.
I think some of the mothers you describe have had another advantage from birth.
I never knew how to eat well. Some of the mothers you described come from families where wholemeal bread, fresh vegetables, water (not fizzy pop) were the norm.
My own childhood dinners consisted of chips, crisps chocolate, frozen convenience meals and other junk. My mother worked two cleaning and a bar maid jobs and I was well aquainted with the local chippy.
My mother also has a poor relationship with food and diet this has fed in to my own issues. When my kids were small my mother would try to ply them with sweets and chips (while starving herself) and I worked hard to stop the cycle.
But even though I know how to eat properly now, I am still overweight, due to my complex relationship with food (from childhood).
Also DNA plays a huge role. My DH is skinny as a rake, can eat anything and does no exercise. One of my twins has inherited his metabolism and the other, mine and at 13 there are differences in their weights, with one still being underweight no matter what he eats.
But you can do this OP. I did lose the weight via Weight Watchers and kept it off for a while when I was made redundant and had more time to meal plan. Now, the stress of my job and home life has now seen me pile on the pounds.
It's easy for me to blame lack of time on my weight gain though. This is why, OP, so much is down to the psychological and emotional, so please take care of your wellbeing and health. I wish you luck but please don't be so hard on yourself. You sound lovely 