Praise be to Allah.
If a man dies and leaves behind wealth, it is to be divided among his heirs as Allah commanded, after paying off his debts and fulfilling his bequests. Based on that, the son asked about here is entitled to his full share of his father’s estate, including the gardens, the houses and everything else. If he dies, his share is to be given to his heirs.
So what you must do is look first at his inheritance from his father, and determine what his father’s estate is, both that which has already been shared out and that which has not yet been shared out. Then this share of his should be given to his heirs, who are: his mother, his full brother and his full sisters (of whom there are four). As for his brothers and sisters on his father’s side, they have no share of his estate, because they are blocked by the presence of the full brother.
Based on that, his mother receives one sixth and the remainder goes to his full brother and full sisters, with the male getting the share of two females.
And Allah knows best.