Old People are not animating

[Zuperbuu]

Before I get into anything: Yes, I have installed FNIS and its dependencies, and ran GenerateFNISForUsers.

I reinstalled Skyrim recently to a new computer and started re-downloading my favourite mods and updating them to the newest versions, I even migrated to using Mod Organiser since on my old rig people constantly told me to start using it instead of doing it manually.
Once I got to installing FNIS PCEA2 things seemed fine; I tested my game after every mod I installed just to be on the safe side, and everyone was animating.
Then I installed RS Children Overhaul and suddenly all the children stood in their default "T" positions, even after I ran GenerateFNISForUsers, so I reinstalled RS Children again and suddenly they worked...then the Old People started doing the T Pose instead, they could be spoken to and their face fully animates, it is just the bodies that don't.

I know everyone and everything except the old people use the new animations I have installed, plus any original ones as well. I don't understand why RS Children would cause this since it doesn't even modify the Elder People Race, so I am at a loss.

Here are a few things I have already tried:
Reinstalling RS Children (again).
Reinstalling all animation mods one by one and GenerateFNISForUsers each time.
Getting Steam to verify the games cache/files, it always detects something as missing and says it fixes it.

FNIS does not display any warnings or consistency issues when prompted to do so. I have made sure to test my game immediately after verifying the games files, but the old people are still broken.