Hi. I've done a few rounds of Insanity and the only workouts you double up on in Month 2 are the Fit Test & Max Interval Circuit and Max Cardio & Cardio Abs. You can split them up, but it's definitely doable to do them together. The workouts are about 20 minutes longer, but as you know the Fit Test and Cardio Abs are pretty short.
Just some advice: do the Fit Test first before Max Interval Circuit and not the other way around because that workout is a beast!
Month 2 is definitely tougher, but you'll feel great when you finish--good luck!