It is definitely really hard. At the start My colleague and I were scoring around 10 points on average as well. Your brain needs to keep track of two objects at once and the fact that shooting with one character messes up your position on the other is something that it only slowly gets better at.
Our music guy had this crazy unachievable score of 55 which was unbeaten until yesterday, where I got all the way up to 60 :D