Possibly, but the photographer usually owns the copyright. Confirm who took it and whether the family can grant permission.
Works by U.S. federal employees are generally not copyrighted, but state and local works vary, and files may contain third-party material.
No. Credit is good practice but does not replace permission or a sound fair use basis.
The purpose of the use, the nature of the work, how much is used and the effect on the market for the original.
Usually only with permission or a strong fair use basis; many publishers offer licensing for archived images.