According to Shariah, when the child turns 7 the right of nourishment goes to his father. Hence the father may take the custody of his son with wisdom and keep him with himself. The mother should not oppose it. We could not understand your matter why your wife stays in her mother’s home and does not want to come to your home. What problem does she have with her husband? Whether the wife comes or not in each condition the expenses of children i.e. food, drink, medicine, treatment, clothes and education are levied on father. At a time when the financial condition of nana is weak then the father should take extra care of two little ones. You should solve the matter through mediation of some influential personalities with your in-laws so that the wife could live with her husband.
Allah knows Best!
Darul Uloom Deoband