What is the ruling on an investor stipulating that the marketer be a partner with him in the commission or that his son be included in it?

There is no objection to investing in a company that engages in permissible activities and does not deal with usury (riba) or other forbidden things, provided that the work of the investing marketers is free from deception and fraud. As long as the marketer's inclusion of the investor or his son in his commission is by mutual consent, the transaction is essentially the marketer waiving a portion of his commission to the investor, and there is no harm in this.