new quantity of one product changes the quantity of related products

[NutsNuts]

Hi, Badly need a hint for a function in virtuemart. On product page, if one enters quantity for product, that should change the quantity of other "recommended" products that come with it. Want to use it in charity, where one chooses quantity of one product and that should change the quantity of boxes/containers, the quantity of labor hrs he/she will need to have the product dispatched form warehouse. "I am saying "recommended" because those quantities, on the "main" and also "dependable" products should be changeable. And also all of these should be still changeable and listed in the cart and his/her order form. How do I do that? Can;t get it work with custom field or child/parent features.. God Bless.