Why must you characterize the desire to embrace the country he's in (rather than yearn for the country of his grandparents) as self-hate? Why must you write as if the behavior of all three in this domestic drama--father, mother, son--is uniquely Mexican?
Go read novels, see old movies, about the immigrant experience whether Italian, Polish, or (like my background) Swedish and you will hear the same stories. There invariably will be, within the same family, at least one child who rejects his/her background and wants to move on along with one or more who is perfectly happy in his/her heritage. It's got to do with individuality, just one element in the human condition.
If the father is truly rejecting his child because he's not blond and blue-eyed (as I assume the mom is and that's what he thought she'd produce) of course that's both hard-hearted and ignorant on his part. But studiously insisting that her child learn everything Mexican is foolish too. Why not see where he naturally gravitates? Sounds like both parents are visiting THEIR relationship issues onto their son.
You say the father's parents choose to speak English and you know more Spanish than your child's father. That was exactly the situation in my own Swedish background. My mom -- way back in the 20s -- deliberately moved out of the Brooklyn ethnic neighborhood because she wanted to be so good at her English that she THOUGHT in English. My father acquiesced in the move but always regretted he basically could barely speak Swedish by the time he was 50 and wished that we children knew at least a few words of that language.
Friends back in Brooklyn we saw occasionally over the years DIDN'T speak as good English as my mom--no doubt about that. I observed that all of us--those that moved and those that didn't--kept up Swedish Christmas customs and food as well as sometimes attending Swedish dances.
To characterize my mom as self-hating is just plain silly. It's two different ways of reacting to life. When she moved to America she was making an irreversible decision. Said she cried herself to sleep every night for six months and then it was over and she relished being "Amercan" and (she said) had no desire to ever go back there. My father remained sentimental, nostalgic, and if he could have afforded it WOULD have paid a visit to Sweden.
I repeat--it's two different ways of reacting to life. Relax, leave your kid alone for a few months and try to observe what HE does when not pushed and pulled between parents with different views. Probably will select somewhere in the middle I suspect.
Three of us children visited Sweden as adults more than once and found it wonderful--the Smoland my mother re-called as very poor and something like living in poorest part of West Virginia we found (maybe it's socialism?) to be lovely, prosperous, with stone fences--looked something like upscale western Connecticut.