Access music from old iTunes account
The very easiest way, which it sounds like you need!, would be to burn CDs of your old songs, by signing in to each account, by making a playlist and then selecting, burn playlist to disk.

To access the music from your first two Apple IDs you just need the user name and password from each one.  Reset your password so that you know the current password for each... make it something random and long that you just write on a piece of paper, and throw away after you re-import the songs into your current account.