Do the Scions know? (Spoilers)

[Iscah]

Though G'raha's is a bit odd because, the alleged 9th fragment was an alternate him.

If you're meaning that his ninth fragment is "the Exarch", it's more complicated (but also more simple) than that.

As his younger self, he has the same eight fragments as everyone in the Source.

As the Exarch, he has lived through the Eighth Calamity and been rejoined to his ninth fragment, an unidentified person from the bad-timeline version of the First. (That person is still out there somewhere in the good-timeline version of the First that we visit in the game.)

With the two versions of his soul merged, the rule seems to be that "duplicates don't count" so he ultimately has nine unique pieces: the eight that both versions possessed, and one extra from the Exarch. If the First was somehow rejoined at this point, he would receive a second copy of that ninth soul and his total count wouldn't go up.