Is the gift given to the mother and siblings, excluding the questioner, and the questioner's deprivation of inheritance due to his dispute with his father and on the pretext of his father's fear of him selling his share, considered legally valid, given the existence of a document proving the questioner's right to shares of these properties after the death of the mother and the youngest brother?

Obedience to parents is obligatory in matters of righteousness. Neither of them has the right to order their son to divorce his wife, and the son is not obliged to obey them in this. What the father did by registering properties in the names of some children and documenting shares for the son is considered a will, which is not valid for an heir. These matters should be resolved through understanding or via the Sharia courts.