How to hack a twitter account?

[Twilightly]

I know this sounds weird, but my high school sorority has a twitter, facebook, and instagram page. I am now in charge of these things, but I have missed placed the passwords and no one has a clue which email was used to set up the accounts. (I did not set up any of them, they were pre-made then handed off to me.) Is their another way to recover passwords? Is it even possible that I can hack into them and change the passwords? I have facebook logged in on my computer, but I don't know the password and need to change it. The others I have never logged into.
No one else knows the passwords somehow not even the person who was in charge of the accounts b4 me.
Help ASAP please.
Thanks in advance.