How should a father's pension be divided between his medical expenses and his wife, especially since she refuses for him to live in her house and she has a son?

If the house belongs to the father, the son's wife has no right to prevent him from it; otherwise, she would be disobedient (nashiz) and would not be entitled to maintenance (nafaqah).

If she does not prevent him from the house but neglects his nursing, then nursing is part of her service, and its ruling is like the wife's service to her husband: According to the view that a wife's service to her husband is obligatory: she would be disobedient (nashiz) by neglecting his nursing, and she would not be entitled to maintenance. According to the view that a wife's service to her husband is not obligatory: she would not be disobedient (nashiz), and maintenance for her would be obligatory. If she neglects the service due to an excuse (illness or incapacity): she is not considered disobedient (nashiz) and is entitled to maintenance.

As for maintenance: If the money suffices for everyone: the wife is given her maintenance, and the remainder is spent on the father and the son in need. If the money is not sufficient: the father is prioritized in spending on himself first, then he spends on his wife and son from the surplus, with a difference of opinion on which one to prioritize (the wife or the child) when maintenance is scarce. The evidence for prioritizing one's own maintenance: the hadith: "If one of you is poor, let him start with himself; if there is a surplus, then for his dependents; if there is a surplus, then for his relatives," and the hadith: "Start with yourself and give charity to yourself; if anything remains, then for your family."