Is it permissible to deal with the mother of orphans who disposes of her orphaned children's money and buys things for them with it, or is it obligatory to verify her guardianship over this money?

The mother of an orphan has no guardianship over his money to manage it, unless she was appointed by his father, or designated by the ruler, or if there is no one else to manage his affairs except her in the most pressing circumstances. There is no objection to engaging in buying and selling with her, and the questioner is not legally obligated to inquire about the father's permission or the ruler's designation.