They got him drunk and had sex with him. I don't recall reading where they were commanded to do that.
I didn't say they were "commanded", did I? What the fuck does being "commanded" have to do with the act anyway?
Genesis 19:30-38
21st Century King James Version (KJ21)
30And Lot went up out of Zoar and dwelt on the mountain, and his two daughters with him, for he feared to dwell in Zoar; and he dwelt in a cave, he and his two daughters.
31And the firstborn said unto the younger, "Our father is old, and there is not a man on the earth to come in unto us after the manner of all the earth.
32Come, let us make our father drink wine, and we will lie with him, that we may preserve seed of our father."
33And they made their father drink wine that night, and the firstborn went in and lay with her father; and he perceived not when she lay down, nor when she arose.
34And it came to pass on the morrow that the firstborn said unto the younger, "Behold, I lay yesternight with my father. Let us make him drink wine this night also, and go thou in and lie with him, that we may preserve seed of our father."
35And they made their father drink wine that night also. And the younger arose and lay with him; and he perceived not when she lay down, nor when she arose.
36Thus were both the daughters of Lot with child by their father.
37And the firstborn bore a son and called his name Moab; the same is the father of the Moabites unto this day.
38And the younger, she also bore a son and called his name Benammi; the same is the father of the children of Ammon unto this day.