Is the husband sinful if he temporarily delays procreation due to debts and poor financial circumstances, knowing that he does not intend to be content with the two existing children and desires to have more children in the future, while the wife wishes to conceive now due to her advanced age and health conditions?

It is not permissible to delay conception for fear of poverty. One must trust in Allah's provision, for every newborn has a predetermined sustenance. Children are also a means of provision. Furthermore, the wife has a right to bear children, and it is not permissible to use any means to delay it without her permission.