You may file a return for a deceased person.
You will need to create an account for them to file.
You most likely will need to file by mail unless you have access to their 2015 return.
You will need the 1040 form (EZ, A, or 1040 Long Form) they used and the AGI, to file electronically.
For more information follow this link:
https://ttlc.intuit.com/questions/3441826-filing-for-a-deceased-person
In the Personal Info Section, the last box
I'm preparing this return for My Son, who has passed away
needs to be checked