So when I try to move the r stick up it does the left trigger action, such as aiming when...

Yeah genius THATS what iam sayin, How it is you CANT see that all of these actions are TOO close to each other, is amazing! I have to spell it out for you step by step,
1. the controller action for prone is to press the R thumbstick
2. the action to aim is to move the R stick an Finally 3. the action to Fire weapon is the RIGHT trigger or RT.. together YES ocassionally this can cause random accidental activation of prone when pulling the RT am aiming the R thumb stick
!

It said click "update" on the help thing but it didn't show up on my xbox

Have you run the steps in Update xbox wireless controller? All controllers you use need to run the firmware update.

The uSB method is my preference.

When you aim in with the left trigger, press in the left analogue stick

It does seem possible. I don't play Red Dead multiplayer much, but have not seen anyone modding in there. He was probably using the auto aim assist. Just use the left trigger that targets the chest of an enemy. Bump the left stick up a bit to get a head
shot.