[AngelicaDeAlquezar]

1) No. It is a verb that needs an indirect object pronoun because if you say "lo tiraron", it means he was the one being shot, not a bullet at him.

2) "Morirse en la raya" is an idiom. It means to commit yourself to do something and die fullfilling your duty.

3) The cause of their death is not the fact that they had been bandits, but they died because they were men, and all men die.
The choice of the subjunctive sets a sort of time frame: they had been bandits before dying.