Man, I have gotten legitimately lost in this song list at least twice.
One thing to keep in mind about double/triple inputs is that the game usually hints at the buttons to push depending on the screen position of the input -- they tend to be laid out roughly the same way the arcade buttons are (so triangle, square, X, O, going left to right). So if you have a double input and you see icons on the far left and right, you probably need to hit triangle and circle. This isn't always the case (and sometimes they chart things to intentionally mess with you), but it's consistent enough to keep in mind.
One thing to keep in mind about double/triple inputs is that the game usually hints at the buttons to push depending on the screen position of the input -- they tend to be laid out roughly the same way the arcade buttons are (so triangle, square, X, O, going left to right). So if you have a double input and you see icons on the far left and right, you probably need to hit triangle and circle. This isn't always the case (and sometimes they chart things to intentionally mess with you), but it's consistent enough to keep in mind.