The elders thought they could pass the throne to the rightful heir now, after all, even the elders were happy with the situation considering the firstborn princess of the previous king had only given birth to two daughters and they all had wanted a 'king' to lead them, as people with an archaic mentality, it has been very hard for them to get instructions from the previous Queens!
They didn't need to follow the royal blood, the current kin and prince were accepted by the masses and the current queen was still the princess of another country... they could adapt to a new regime, even the previous king was in for it!!
But of course, the princess was had wanted her girl to be the next in line heir and hence all of this happened.
Her husband loved her a lot and has been turning a blind eye to her, he was hopelessly in love with her and even though he loved his 'younger' brother... he still, chose to remain the foolish prince.