File single 2016 now needed to file marry 2017 he had a stroke what should I do

If you were married on Dec.31, 2017 file jointly.  If he cannot sign see "injury or disease prevents signing"

https://ttlc.intuit.com/questions/3049864-my-father-can-t-sign-his-tax-return-because-he-had-a-stroke-and-in-now-mentally-incompetent-should-my-mother-sign-as-wife-or-guardian