Ability to Calculate Ingredients total in Product Development

Out client is into beverages and they build FG with 1 Pound and expectation is when they add the ingredients under Structure, system should show them the total of all the ingredients as it should be always as a total of 1 pound.

it should not be more or less than 1 pound, If it is then User can manually adjust the qty to make it as 1 pound in total.

We are trying with Sandbox however no success yet. Is there any other option to achieve this?

Below one sample example, In actual Business scenario they have 20+ items as child.

Regards,