In my opinion, p90x is for those already in shape and only to get more muscle texture and also requires a bunch of equipment. Insanity however seems like a program that focuses on fat burning rather than muscle building and does not require any equipment. Insanity is a 60 day program and p90x is obviously a 90 day program. If you were to start tomorrow or monday, you could basically do both and be done months before your brothers wedding. I would personally start with Insanity first, which I will be starting next week, due to the reasons in which I have mentioned above. just my 2 ¢.