So i just beat the game tonight and it was THE BEST KH game!!!! But i had one major question that i still quite don't understand. So if Riku was put into Sora's Dreams and unlocking the sleeping keyholes in Sora's dreams then how were they both able to help each other do things together like collecting the Sound Ideas in the Symphony or Sorcery etc... Can someone please try to explain this to me because i am totally lost when i try to come to an conclusion about it... thx

Riku was able to help sora because it was sora's dream all along. Think of riku as like a backstage dream editor/helping hand

Yen Sid said something about dreams being deeply connected, so if that is true one thing that happens in one dream can effect another, like when Riku stopped the trap in the musketeer level and Sora saw the effects of that in his version of the world