Is it permissible to demand 15-20% of the real estate loan amount in exchange for using one's name and services, after the completion of construction and settlement of dues, especially since the claimant's father has children and wives other than his mother, and he is wealthy but stingy with himself and those around him?

A father's utilization of his son's name in a project does not constitute ownership for the son in that project, because the son merely lent his influence (jah), and he is not permitted to receive compensation for that unless he incurred actual financial cost or effort. In such a case, he is allowed to take the prevailing wage (ujrat al-mithl), unless he volunteered his effort.