Ideally you don't need to resort to conditionals, but if you do, then there is no shame in drawing. Basically, you want to do whatever is fastest and gets you the right answer.
You pretty much have to rely on the conditionals, specifically how they say that if 1 and 3 are different, then 2 and 4 must be T, or how if 3 and 4 are T then P1. If you need help with a specific question I can try to help specifically
It will not be correct to diagram it as bi-conditional since it is "Only if" which indicates necessary condition. "If and only if" indicates a bi-conditional situation they are talking about.
... until you can do complex conditionals effortlessly, know how to logically ... , know the rules associated with conditionals and or rules for LG ...