Your prince/princess translations are off, as they don't refer to "children of royals", just plain "children", as you correctly translated the neutral form and the grand-counterparts.
Oleth-til/-vol/-yen/etc. function exactly the same as cyne-til/-vol/-yen/etc. so an oloth-vol is the leevoth of an olaith-til, but the sevol of an olaith-yen.
As such, your "crown prince/princess" translation is particularly inaccurate, since the oleth-til is the eldest, while the rules of succession call for the youngest oleth past their olesata with a beirvet (hence why the olaith-yen became cynai among the group of three oleth).
As for "tale-sevel", if you had one, you could be said to be their "sevel-oleth", or more simply their "seilet".