Friday's dad and the Spaniard go off to the mainland to find help later in the story, just before Crusoe & Friday find the shipwreck and leave for home. Without Friday's dad or the Spaniards. Oh dear - they can't have been too pleased...
This isn't a slip-up. Crusoe and his men that he rescued knew they were leaving the Spaniard and his father there. After they escaped, Crusoe was wondering how the Spaniard and his father would fare on the island with the three criminals. They left because they were anxious to get home with the new men that were there and the Spaniard and his father could have been lost at sea, which would cause supplies to run out on the island.