I don't think the OP needs to see the stepgrandchildren as hers, because they aren't. They are her DHs GC.
OP.... you could have and should have written your post without mentioning her weight, comparing her to her mum or the state of her house. You just came across as nasty for saying that... and it looks like you hate her DM too. You sounded really venomous in your description of her. Her mum has nothing to do with this situation. She's your DHs Ex...why did you feel the need to bring her into this?
Mentioning the above is why you're getting a hard time. You must know weight is a very sensitive issue and attributing it to laziness will never go down well.
As independent posters, ppl are drawing the conclusion, that if you come across like this about her (with hatred towards her), then you're bound to show that in person in some way or other.
If I knew someone who is as you describe your SD... like I said earlier, I'd be leaning to think she has something going on.
You don't mention her having a DP/DH... that could be an issue. Being a single parent is difficult for some people.
She may be struggling with controlling and disciplining her DC..hence they think jumping on furniture is acceptable behaviour.
She could have mental health issues, causing her to be moody.
Most ppl would have stopped to think something else is going on.
The issues were her rudeness, her DC jumping on furniture and her general moodiness. That's what you should have focused on.
I also don't think you should expect a guest to offer to help you in the kitchen...you invited her...she probably wants a break.
She has a father and siblings... in most normal loving families, one or both of these relatives would show concern about her moodiness and try and find out what is going on. I know if I presented in such a way, my family members would be very concerned about me.