How to troubleshoot wiring that trips AFCI breakers?
You don't need to decrypt breaker indicators.  The fact that two breakers trip is all you need to know. 

Why would one thing trip 2 breakers?  These two circuits have their neutrals crossed, tied together, or interacting in some way.  Perhaps one device which takes its hot from circuit 1 is taking its neutral from circuit 2. 

Hots and neutrals are supposed to be monogamous -- they're only supposed to partner with each other, ever.  That's always been in the code.  But until recently, crossing neutrals "worked" - it didn't cause any detectable problems. 

What happened "recently" was adoption of GFCI and AFCI.  Those absolutely require hots and neutrals be monogamous.  If current comes back on the neutral in an unexpected way, that makes it trip.  

So you have to go through each circuit, look closely at every box, and find the place where a neutral doesn't match its hot.  It's a tedious job, and I've done it.  If it helps, get gray tape and put it on the neutral from one of the circuits.  Gray is an allowable color for marking neutrals.