Danny's gun makes no sense

I don't get this Danny-character. I know his name is something else, but I just call him Danny for simplicity.

Why would he point a gun and tell them he's 'stealing' the stone, when the stone LEGITIMATELY (well, from some perspective) belongs to him? Why would he point a GUN at them, when he still has Joan's SISTER, so they can't do anything to him, and have to do anything he says?

Also, he has a gun.. it's HIS car.. he has the stone - HE HOLDS ALL THE CARDS. All he has to do is say 'all right move to the side', get into his car and drive away.

What does he do instead? He starts RUNNING? What.. why? It's HIS CAR! It's HIS JEWEL (stone)... he has a .. did I mention, GUN!

Why the heck would he, that holds all these cards, have to start RUNNING, when he could just tell them to 'stand over there' and sit in his car and drive away?

"So the movie can happen", I can almost hear Ryan George's voice say in my head.

Sigh.

This Danny-character, holy COW is every single decision he makes weird. Why does Joan have to call Danny's brother about her sister, when Danny could just WALK TO HER and they could talk, she could give him the map, he could then complete the transaction and drive to a safe place, call the bro, tell they have the map, then the bro would release the sister...

I mean, anything LOGICAL or 'realistic' or 'expected'.. just doesn't ever, EVER happen in this movie, especially with this weird character.

It's ALMOST as if the whole 'brother' thing was written afterwards and added later, and Danny's character is supposed to be just some stranger trying to get the map. That's the only explanation I can think of that would make some of this make some kind of sense.

Otherwise, it just makes no sense. Danny is supposed to meet her and get the map so they can then release the sister. Why does he act like he's just some weird criminal thug that has no idea about her sister whatsoever most of the movie?

This character drives me nuts, because his actions make no sense...