It has worked out well for me and friends and family member to see the same therapist. She even handled it well when there was an upset with a good friend who was her client. A good therapist that works with couples or families should be able to handle seeing you and your brother. They should also be able to work with any feelings that come up for you and your brother sharing him/her. I would even haul siblings and parents into therapy with me when they were only in town for a hot and a cot.