AITA for telling my brother & SIL to put their daughters on diets

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The original was posted on /r/AmItheAsshole by /u/ThrowRAclockinout on 2023-10-07 02:15:47.

My(33M) brother( 37M)and his wife(36F) are pretty open books when it comes to their issues. The issue they face is they have 2 daughters(15F, 17F) that are obese. Apparently their doctor brought this up and the school nurse raised concerns to them as well.

While I was visiting them, and when the girls had gone to their rooms, they began venting to me that they feel like their daughters run the house. They don't do chores or pitch in with anything. This led to them telling me the girls snack constantly. They asked if I had any advice

Now, I'm not a parent, but, my brother & his wife are both pretty receptive to get advise from almost anyone. They are just looking for any ideas.

I said, that if I were them, I'd reassert myself as an authority figure, write the chores out, make sure they get done, and make sure they know what happens if chores don't get done.

As far as the snacking, I told them if it were me, I'd just throw the snacks out, go cold turkey. I added that, on top of no snacks, I'd advise they take seriously what the dr. and school nurse said, and told them it's time to put their daughters on diets.

My SIL argued that they'd be miserable on diets. I argued that, given each of them is 210+, they're already miserable most likely. This appalled them both.

AITA?