still rtbs need there own space in a tank with a little cave or hideing place which he can call his own.also tiger barbs, 'other tetras', maybe neons, need to be in bigger groups as they are schooling fish.and ive got to say im very surprized if your betta is ok, i know if i was a betta i wudnt want 3 nippy tiger barbs and loads of little teteras around me harrasing me.
i think you should get the betta out of there asap as its for its own good.all he wants is a bowl or tank of a minimum of 2 gals to live in and possibly a heater and he will be fine and happy.