So i think it was implied that Yen Sid had Sora and Riku time travel to Destiny Islands at the start of their journey, but were they able to time travel because of Yen Sid's magic? We know from YX that one can gain the ability to time travel by freely giving up their body. Sora willingly gave up his body to save Kairi, and while Riku probably did not want to lose his body he DID let Ansem into his body which caused him to lose his body later. So by the laws of the KH universe can sora and riku time travel on their own?

if they can go to other points in time can they also travel around the worlds of that time period? cuz then Sora could like see aqua again and maybe find out where Ven is by following aqua around. 

But does Sora even know who Aqua is and does anybody even know that she's the one who hid Ven?

But does Sora even know who Aqua is and does anybody even know that she's the one who hid Ven?

well mickey should at least know that aqua hid vens body and Xemnas knew that there was a secret in castle oblivion so who knows.