A few weeks ago, I purchased Destiny 2: Shadowkeep on steam as an early birthday gift for my younger brother. However, as he also switched over to PC for his birthday, He ran head-on into what is apparently an outstanding issue with how cross-save interacts with Season passes. This resulted in his season pass/1000 silver being deleted, with no way that I can tell, to get it to his characters (If he cancelled cross-save I believe it would require him to start from scratch with new characters to keep the season pass.). According to a Kotaku article, this issue has resulted in refunds/reinstatement of the season pass when Shadowkeep launched. Would he be able to receive this if evidence of purchase and what not was provided?
Did you purchase the Shadowkeep expansion under your account and gameshare licenses, purchase it as a gift, or your brother a gift card to purchase it under their own account? Did your brother activate Cross Save before they logged into their Steam account and accept the warning banner about the Season Pass being redeemed?