YA/ New Adult Medieval Fantasy. River journey with the incarnations of cursed siblings. Magic and battles. Read in 1990s?

[Naomi]

What's the name of this book I read years ago, (possibly the 90s) about three? four? youths who journey down a river to go trading.
They meet three people who are the reincarnations of three enchanted siblings, who, ages ago, were blessed / cursed with special powers. The woman can bewitch any man, the one brother is a great warrior who can command armies, and the third brother can find any road or path out of or into anywhere.
In the story, there's a blind king who's the father of the woman who reincarnates to have the enchanting power, and there's a knight called Toran (or possibly Torin) and his friends are conspiring against him.
It's a medieval fantasy book, with magic and battles.