Exactly! just becuase theyre from the same family doesnt mean theyll get along... and if the betta looks unhappy either get rid of the other tank mates and get cories, or give him back to the store and stock your 10 gallon correctly. A pouting fish in the back corner obviously is not a happy one and should only be kept in those conditions for sa short period of time (a few days TOPS) for you to figure out what to do. Please dont make the betta have to deal with other fish that it considers a threat, its not right...