Online Information for Demon Souls and Demon's Souls Remake provides details on online play and how player trade works. You can also find a summon range calculator to assist in matching co-op and pvp players. Be mindful that the Demon's Souls Remake of 2020 increased the amount of online players to 6, which means mechanics are not the same as the original game.
Online
Black Phantoms ♦ Blue Phantoms