This is unacceptable and crap. No one should be body shamed. My brother who is a phenomenal gymnast was bullied off his team and the coaches let that crap go on. I would try to level with the coach 1on1 in private if possible.
If things don't shape up, I would check if there is a local adult running program you could join up with for the summer. Many specialty run stores have them. Strava is also awesome as it is very goal and data oriented - also a positive environment were we encourage one another.
If you want to thin out, do it for you and not for them.
As a 32 year old with slower metabolism who went from 230 down to 170 (still going) in the course of less than year, here are some things that worked for me.
Weight loss is 80% diet and 20% activity. It also is literally a game about calories in / calories out. Anyone who says otherwise is blessed with an awesome metabolism or is lying.
The trick to not starving yourself is to seek out foods that have low calorie density and make them priority. The best option is to target veggies and fruits. They will help you recover from runs faster as well. Don't think so much about depriving yourself or giving stuff up, but instead shifting focus over to foods that are going to make you strong. With that perspective, you aren't restricting pleasurable foods, just eating them less frequently.
My go to veggies are sweet potatoes, steam-able broccoli (I load those suckers up with franks red hot) and beets. Finding out that sweet potatoes could be microwaved was a game changer for me. My diet is literally 70% produce at the moment, but I had to slowly ease into it. I personally don't eat meat, but lean chicken / fish is a good lean protein option.
The more you can shift your intake over to plants, the easier it is to manage everything as they are much more filling. Most processed foods are engineered to be calorie dense, be addicting and not to be filling. Sadly, the American diet dooms a person to be overweight :/
IMO Akins / Paleo / Keto would not be wise as you are a cardio athlete and carbs (the good plant ones) are key for fueling your runs.
Best of luck on YOUR running and fitness journey - not theirs,
Just avoid the temptation to be a jerk 10 years later when the tables turn and they are the ones less fit than you. :D
-Tyler