I'm sorry for your loss. You can file a joint PA return for your grandmother and grandfather. Just be sure to mark that your grandfather is deceased. According to the PA Department of Revenue in How do I file a PA income tax return for a deceased taxpayer?
Effective Jan. 1, 2013 a joint return can be filed by the surviving spouse and decedent when a spouse or taxpayer dies during the tax year if:
- The decedent did not previously file a return for the tax year; and
- The personal representative, executor or administrator has not
been appointed by the time the return is made, signed and filed; or
- The fiduciary of the decedent consents to the filing of and signs the joint return.
