How can one act Islamically regarding a project that was built on land ceded by heirs, funded by an interest-based loan, with the intention of making it permissible after the death of the borrowing partner, taking into account that he is the sole provider for his orphans?

We ask Allah to have mercy on your brother and forgive him for taking out a usurious loan. We advise you to care for his children and work to make the project successful, provided that its activity is permissible. Financing the project with a usurious loan does not make it unlawful or its returns unlawful, because the loan, once received, becomes the property of the borrower and a debt upon him, with the borrower bearing the sin for dealing in usury and obligated to repent.