Is it permissible to renew the intention now for gifts I previously gave them, or for money I placed in their bags without their knowledge, and consider it a restitution for stolen money?

The intention must precede or accompany the commencement of the act. The gifts and money you gave to the heirs with the intention of returning stolen property are considered sufficient to absolve you. As for what you gave without intention, it is considered a gift, and its intention cannot be renewed for the stolen money. You must give out money in its place so that each individual receives their share. What must be returned in the case of theft is its like if it is a fungible item, or its value if it is a non-fungible item.