The Fallen Monk Pirates seem to share the same dark skin tone as their captain, Urouge, and even wear the same brown monk robes. It is unknown whether Urouge is the only one to have come from a Sky Island or not though it seems likely as he is the only one so far shown with their trademark wings.
It can be assumed that they are strong because of their captain's high bounty and the fact that they made it all the way to Sabaody Archipelago. Urouge is also noted as one of the super rookies who appeared on Sabaody Archipelago before the Battle of Marineford. Despite Urouge being incapacitated, the crew was still able to escape from Kizaru's attack. A further testament to the crew's strength and their miraculous knack for survival is the fact that their captain defeated Charlotte Snack, a man with a 600,000,000 bounty on his head and one of the Sweet Commanders of the Yonko, Charlotte Linlin. When they incurred the wrath of the Yonko, they were forced to fight Charlotte Cracker's entire fleet, and although they were defeated, the crew managed to escape alive once again and were last seen recovering on a Sky Island known as the Ballon Terminal. Their presence on a sky island also indicates that the crew has a method of traveling to and from the island clouds.
On a Sky Island, Urouge was recovering from wounds he had received. The crew told him that someone was approaching and that person was the Yonko known as Kaido. When Kaido decided to jump from the Sky Island, Urouge did nothing to interfere and just prayed for him as he fell onto the island below.