He’s a criminal like his brother. He sounds like a nut because he’s talking nonsense that he hopes will distract investigators from looking too closely at the source of the family money.
The older brother was a high functioning psychopath like their bank robber father. The younger brother is just a crook.
Little brother tells just how his big brother would get the guns up to the room. Pay a bell hop to use the little gold cart, simple as that.
Little brother also admits to doing whatever the killer brother wants for monetary/food gain. Somehow I bet he’s going to be implicated in helping his criminal brother. Maybe nothing significant and possibly unknowingly but it’s probably one of the reasons he is so fidgety/weird.
I wonder how many guns were purchased in the brothers name?