KS seems to have forgotten that, as head coach, he first has a duty to his family (to remain employed), then to BYU (to win as many games as possible), then to BYU's fans (yes, fans actually matter), and then finally to his coaching staff.
Since KS has not been running the program in a way that is fulfilling his obligation to the first three groups, he should either fire Tuiaki or submit his own resignation.