Sentence Correction

Greatly influenced by the Protestant missionary Samuel Kirkland, the Oneida was the only one of the five-nation Iroquois League who sided with the colonists during the American Revolution.

A) Same
B) was alone of the five-nation Iroquois League when they sided
C) alone among the five nations of the Iroquois League sided
D) were the only ones out of the five nations of the Iroquois League in siding
E) only of the five-nation Iroquois League had sided

OA-> A

My question is, little bit aside from the question itself though, that in "The only x of the Y ~ who(or that whatever matches with x and y)~ ", which one -btw x and y- is modified by the relative clause?

1. Y - because it is more close to 'who'
2. simple ambiguous btn X and Y and treated as wrong in SC
3. what if the second 'the' in front of Y is removed? Then, the relative clause modify X due to 'the' in front of X, even the relative clause can modify Y in meaning?

Then reason why I ask this is because I've heard that noun proceeding relative clause and connected with preposition even the noun is not the one right in front of relative clause, can be modified by the relative clause and that a noun, among some of proceeding nouns, which has "the" in front of it , is firstly modify by the relative clause.

Here you can the discussions had on this.

https://www.beatthegmat.com/gmat-prep-sc-t47874.html