|Please keep in mind that this is only one opinion and you did ask for grammar help. Overall, it was good and these are only very minor picky details.
The sun leaned (word choice, can a sun lean? Maybe try press down or beat down?) close and I could feel (present tense while the rest of the paragraph is past tense) its scorching breath on my neck. My eyes had turned to rocks in my skull that my eyelids dragged themselves over time and time again as my throat became a desert canyon. (Run on sentence. It would flow better as separate sentences. My eyes had turned to rocks in my skull. My eyelids dragged themselves over time and time again the jagged crevices. My throat became a desert canyon impairing all sound (maybe rephrase so they don’t all start with “My”)). It was a bitter mercy, for if I had been able to cry or scream I would have broken apart and let insanity rule me as we watched the snow white minivan disappear down the street and take a right turn out of my life. (Same run on comment. It was a bitter mercy, for if I had been able to cry or scream I would have broken apart and let insanity rule me. We watched the snow white minivan disappear down the street and take a right turn out of my life.)
… He spun on his heel, crushed a rock (word choice? If he is crushing rock then it makes him seem superhuman) into dust against the concrete driveway, and stomped into the house...
“Have you ever thought about taking the kids and leaving?” the doctor had asked. “He’s going to kill them.” My mom’s eyes flipped him off in response.(good metaphor but rephrase, eyes don’t flip off, try The glare Mom’s eyes directed in response was as clear as if she had flipped him off? ) How many times had she tried to take us and run? How many times had we ended up back home with that smirk of his? Mom was in a wheelchair and had no family to ask for help. If she tried to run, he promised to find her and gain full custody of her (her children? Are they not his to, or theirs?) children. So She ground her teeth and, even through the divorce hearing when . He slapped on the mask appearing to be Mr. Wonderful, She still kept her composure.
That mask was like the light barb on a dragon fish, just a distraction from the monster lurking behind it. (I’m not very familiar with fish so I have very little idea what this is trying to show.) The monster’s problem that hot afternoon (is it only a problem in the hot afternoon or is it always a problem?) was the loophole in the custody agreement. If one child stayed with him full time, the other two were free. (If this was his condition is it still his problem? More likely it is the child’s problem? This seems like a very odd condition without further explanation, and if it was his condition why is he now angry about it?) … I learned to see victory without the end credits reading ‘Happily Ever After’ (what victory?)…
Favorite line: “We watched the snow white minivan disappear down the street and take a right turn out of my life.”
It’s a very sad and strange story. There are too many details to just convey the pain the child is feeling, but not enough to understand the circumstances of the situation. Maybe more elaboration would be helpful to the reader? You can feel her pain though, good job portraying despair. Just my humble opinion.