It’s difficult to say without seeing the conditions of the fare you have purchased. Your e-ticket should state your baggage allowance. If your ticket says 30kg that is the maximum total amount for each passenger, that 30kg allowance can normally be split in to several bags but the total weight must not exceed 30kgs. If your combined luggage weighs more than 30kg then excess baggage charges will be applied.
If your Star Alliance status permits an additional 10kg then that would mean your total weight allowance will be 40kg, that is 40kg in total - not per bag.
So, if there are two passengers then the combined total weight for both passengers’ bags will be 60kg (30kg per passenger) with an extra 10kg for the Silver card holder if the Star Silver permits the additional.