De är nornerna.
Jag läste just dessa kapitel i går, och bokens text gör det helt klart.
För det första är de definitivt inte Zoryas systrar:
There were three women standing by the tree. At first glance Shadow thought that they were the Zorya, but he realised in moments that he was mistaken.
Men de är systrar:
They looked like a set of Russian dolls: a tall one - she was Shadow's height, or even taller - a middle-sized one, and a woman so short and hunched that at first glance Shadow wrongly supposed her to be a child. Still, they looked so much alike - something in the forehead, or the eyes, or the set of the chin - that Shadow was certain the women must be sisters.
Och en av dem heter Urðr, vilket betyder Past:
The biggest woman, whose name seemed to be Urtha or Urder - Shadow could not repeat it back to her to her satisfaction - told him, in pantomime, to take off his clothes.
[...]
In his delirium, Shadow became the tree. Its roots went deep into the loam of the earth, deep down into time, into the hidden springs. He felt the spring of the woman called Urd, which is to say, Past. She was huge, a giantess, an underground mountain of a woman, and the waters she guarded were the waters of time.
Alla citat är från kapitel 14 i amerikanska gudar , med undantag för sista stycket, som är från kapitel 15.
Så det finns tydligt kanoniskt bevis på att Radhils svar är korrekt och de tre kvinnorna på fältet är Norns: Urðr, Verðandi och Skuld.