Stop the kidnappers in the bank robbery side mission with force or persuasion.
Talk to the Marshal and offer to help.
He outlines the situation that resulted in the Shaw gang holed up in the building and taking hostages.
The situation seems very serious.
you might trypersuasion(seePersuasion in Starfield).
That ends the matter.
It doesn’t matter.
Let Blake give you thebackdoor keyto the bank and you have two options.
You either have toput down your weaponsor make anotherattempt at persuasion, then the door will open.
Inside the bank, it’s all about taking out the Shaw gang.
There are six people in total (top three, bottom three).
It doesn’t matter, they have to die anyway.
There is no other way.
Wipe out the bank robbers and report to Blake for a less graceful completion of the quest.