Мysql запросом?
Зачем в таблице-связке поле id?

SELECT Members.* FROM Members LEFT JOIN members_teams ON Members.id = members_teams.member_id and team_id = 1 where members_teams.member_id is null

Лучше использовать JOIN. Как-то так:
SELECT Members.* FROM Members LEFT JOIN members_teams ON Members.id = members_teams.member_id WHERE team_id <> 1
