If his parent(s) won't give permission for him to be baptized in church, perhaps they would allow a priest to come and baptize him. If that isn't allowed, I would speak to a priest anyway, telling him of your concern for your grandson. Ask him for permission to baptize your grandson yourself. At least that way it wouldn't be done independently of the Church. In any case, it's much preferred that it be done with the parent's permission.
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