Does a son have to spend on his father even if he is rich?
Question

                My husband’s father helped my husband to get married, then my husband traveled to one of the Gulf countries for work. Because he has many debts that he wants to pay off, he is not sending any money to his father. 

Now his father is demanding the money that he spent to get him married, even though my father-in-law is a doctor and has a good income that is more than enough. 

My question is: 

Is it not the father’s obligation to get his son married? What should be done in this situation?.
Praise be to Allah.Firstly: 
The father is obliged to get his son married 
    if the father is rich and the son is poor and cannot afford to get married, because marriage is part of the obligatory spending. Allaah says 
    (interpretation of the meaning): 
“but the father of the child shall bear 
    the cost of the mother’s food and clothing on a reasonable basis”
[al-Baqarah 2:233]
So the father has to get his sons married if 
    he is able to and they cannot afford it. He has to spend on them with regard to food, drink, education etc, because spending is obligatory upon 
    the father. 
Secondly: 
The son does not have to spend on his father 
    unless two conditions are met: 
1 – The son is rich (i.e., he has what he 
    needs and more) 
2 – The father is poor. 
If these two conditions are met, then the son 
    is obliged to spend on his father. Here the questioner mentions that her father-in-law is a doctor and that his income is good. If that is the 
    case then the son is not obliged to spend on him. But if the father asks his son for something, even if he is rich, and the son does not need that 
    wealth and will not be affected by giving it to his father, then he should give it to his father lest he be regarded as being disobedient towards 
    his father. But if the son needs that money, he does not have to give it to his father; he should explain to his father the financial difficulty 
    that he is facing [?} and that after he had paid off his debts and has become financially stable he will send money to his father as much as he 
    can. 
“Allaah burdens not a person beyond his 
    scope”
[al-Baqarah 2:286 – interpretation of the 
    meaning]
And Allaah knows best.