Robert is 76 and married. Does he need to file a tax return? And should his wife file married, filing separate?

[DoninGA]

When you are legally married you should be filing as Married Filing Jointly even if one spouse has little or no income.

[VolvoGirl]

There's a lot more to it than that.  It depends on their income and what kind.  They should file a Joint return which is one return combined for the both of them.  We would need more specific questions.  This sounds like  a homework problem.

Do you need to file a return?

https://ttlc.intuit.com/community/filing-and-paying-taxes/help/do-i-need-to-file-a-federal-return-th...

IRS Do I need to file?

Do I Need to File a Tax Return? | Internal Revenue Service

See IRS pub 501 for filing requirements

https://www.irs.gov/pub/irs-pdf/p501.pdf