...I see absolutely no reason why our characters would spend any amount of time or effort attempting to betray each other. Each character has something that they need from the group which they cannot personally obtain for themselves:
o Sesthorono, Hreeka, Va and Cenotaph are all reliant upon having either high quality equipment and/or regular healing, but are unable to interact with demihuman society in a way that allows them to obtain such things. They need people like Ego, Oolooth or Di'rac to interact with people for them and a cleric, like Meep, to provide healing.
o Ego, Meep and Di'rac, while each able to go into town unmolested, are personally lacklustre combatants who, without a powerbase of powerful combatants like Sesthorono, Hreeka and Cenotaph, would be swiftly killed, imprisoned or banished by good-aligned adventurers as soon as they gained any real prominence.
o Oolooth is a tiny slug that lacks both opposable thumbs and the ability to communicate beyond the 20 foot range of her telepathy. Without loyal and capable allies, she is limited to exerting meaningful control a single enthralled individual at a time, which is entirely too little.
While there is enough redundency in capabilities that any individual character could be removed from the group without the whole thing falling apart, no one individual is able to successfully strike out on their own without being left incredibly vulnerable to wandering adventurers. Anyone that attempts a betrayal, or even rocks the boat enough to forfit the protections and assistance of the group, will have effectively signed their own death sentence.