It's much easier to "hack" the email account associated with their social media accounts; once you're in you can use their email to do password resets on all of the accounts.
Once you have their email address, go on their mail host site and click forgot password. Many times all you have to do is answer a "secret question" to gain access. See what that question is and then get to work on finding the answer, either through research or through socially engineering the target into revealing the answer.