Is it possible to have a full house and straight flush in same hand with only two players?
Certainly.

Player 1 : 5h 6h

Player 2 : 8c 9c

Community cards: 7h 8h 9h 8d 9d

Player one has 5h 6h 7h 8h 9h

Player two has 8c 8h 9c 9h 9d