Queens can only be hatched from "queen eggs". The fact that both Diana and Anna have only one active daughter suggests that only one queen egg is allowed to mature at a time (although multiple queen eggs ca be born ). Queens cannot breed until they develop their "breeding skin", which enables them to successfully mate and lay a clutch. It is possible that queens develop their ability to project a type of scent known as bliss around the same time.
In case where there are two future queens, the first born is the queen the second child is known as the princess or rather lady. in some cases the future queen has her future queen while her sister is still around cause many problems.
There has been king in their history but only six,though these six are considered great kings and now when kings are born instead of them being unholy they are considered great messiahs.