Does the husband’s son inherit from the wife of his father?
If the wife was entitled to the pension, then whatever she took possession of from it became her property alone, and it is not permissible for anyone to dispose of it or any part of it except with her permission.
See the answer to question no. 147802
If she has died and she had saved up some of this pension, then this money and whatever else she left behind becomes the right of her heirs who survived her, and the heirs of her husband have no right to any of it.
The husband’s son does not inherit anything from the wife of his father, so he has no right to this money unless his father’s wife bequeathed something to him.
And Allah knows best.