These are kids. At 19, even the best plan is going to be flawed and incomplete. There are details that aren't even on their radar. My take: they spent all this time planning the actual exposive event with great detail and bought into the movie version of escape afterwards. The older one chose SBC (suicide by cop) when their afterplan quickly fell apart, the younger just ran.
Btw, easier for a single individual making random choices to avoid capture than a coordinated group.