First of all, its strange that you are ranting about monogomy in a story about polygamy, whether real or ficticious, a couple that choses to engage in polygamy cant be held by the same standards as a monogamous couple, it just doesnt work...
Secondly, I said a man who *assumes* his wives would elope on him with each-other, just because they have some bisexual bedroom play, is brainwashed. Of course, no man wants his woman to abandon him & run away with another woman. But your two wives showing each other some affection & sexually pleasing each other, either solely for your viewing pleasure, or because they are really bisexual & enjoy it, isn't the same as them actually leaving you for each other. And the unfounded fear that they would leave you, when at least half the reason they are lessing out, is to excite you, is completely irrational, & shows a lack of confidence in your skills as a lover & self worth as a partner, & lack of trust in your wives & faith in their love for you.