Snicks, I am moving your question back closer to the front of the questions. Hopefully a caregiver with experience with this type of financial issue can answer your question.
Otherwise, you would need to contact a CPA or income tax preparer for an answer. With the recent U.S. Tax Reform put into law, there may or may not be any changes to this matter.
With my Mom, her SS and pension was a total of $1700. IRS had told her years ago to no longer file because she was considered low income because most of it was SS. I would call a CPA and see if he even needs to file.
Otherwise, you would need to contact a CPA or income tax preparer for an answer. With the recent U.S. Tax Reform put into law, there may or may not be any changes to this matter.
It makes a really big difference.