Combine 1 bottle barbecue sauce and dry onion soup mix in a large slow cooker; add pork loin and ribs to the slow cooker. Cover the slow cooker.

Cook on High until meat falls apart, 6 to 8 hours. Transfer meat to a platter; set aside. Set slow cooker aside until cool enough to handle. Transfer the cooking liquid to a bowl. Skim and discard excess fat, reserving 1/2 to 1 cup of the liquid. Wipe out the slow cooker.

Remove ribs from bones; discard bones and fat. Shred pork loin and ribs with two forks; transfer shredded meat to the slow cooker. Add reserved 1/2 to 1 cup cooking liquid and remaining bottle of barbecue sauce. Pour a small amount of water into empty barbecue sauce bottle, shake, and add to the slow cooker. Stir to coat evenly.

Cook on Low for 1 hour more.