How could you says posters have massively taken it out of context, when in your own words -
No they do not consider them their grandchildren in any way.
First of all, you should not be feeling guilty for not telling your parents about your brother's marriage as it is your brother's choice and you may ruin your relationship with him and his family, who all seem like decent people.
Secondly, you should feel a little guilty for saying 'you don't understand why he did it' right after saying he got married in India. He is an adult, he loves someone, they both decoded to get married, don't understand why there is any more explanation required for why he did it.
Third thing is, you and to some extent your brother are conditioned to see your parents as forever authority figures, whose approval should be utmost importance to you and your brother. Why would you brother care for the sex of his child being male, so he could please his parents. So what would have happened if your brother we r had a daughter, your parents would have not accepted her. You can't put everything on Indian culture. There are many traditional Indians, but there are also many Indian parents who love their children and would care for their happiness.
And why should your brother owe them any information or update about his life including his marriage and family if he knows his parents care nothing about what makes his happy and have their own image, prestige, etc which they value more and their son eanting to start his life with an older and single mother would be worth disowning him. They don't own him, but it it obvious ending relationship with own son is easier for them than accepting him with the life he has chosen for himself.
It's a shame that you are okay with your children not being equal to the children of your brother if he was married to someone they approved of. Your children would have felt the discrimination and it seems like you are okay with that. I hope your husband's family love them like own grandchildren. Your family is dysfunctional and to some extent, it seems like you are far more accepting of it than your brother.
Some Indian people have even changed over years and able to change their belief systems for their children and family, so your parents can't be excused.