In the ancestral property the second wife will get a share from the share of the father in law's property and the three children will take their share from the share of their mother. Other than that if there is no will made and it the self acquired property then also on the death of your father in law your mother in law will take one share of the total share of your father in law and your wife will take another share i.e half each in every case. The three half blood sibling of your wife will take their equal share from the share of their mother.
All children will get share
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