When you start out to knit the two stitches together through the back loop, are you coming at it from the top or from the bottom? If you put your right needle into the back of both stitches from the top, pointing your right needle down into them, I don't think it should get all twisted up and too tight to work with.
Also, it helps, as you continue the row, to use your right index finger to hold the stitches on the right needle so they don't slip off.
I'm NOT an expert at herringbone and I apologize if you're already doing this, but I gave it a try and it seemed to work for me. Good luck, I hope you can get it!!