Sarah gave Hagar to Abraham to have sex with. I see no evidence that Hagar was asked her opinion on the matter. Moreover, it seems God was fine with this. Hagar tried running away but an angel appeared and told her to go back. So you see... a slave is property and she can be nailed at will. I was looking through Exodus for hints that females slaves can't be raped, but I didn't see any. I saw that a man could buy (yes, buy) a girl to give to his son, and I saw that if he beat her to death, it was punishable, but rape? Seems to be fine. In fact, hopefully, as in the Old South, the slave will bear offspring to increase her master's wealth.
No, God was not fine with it.
He was protecting Hagar and Ishmael from death.
Yes Sarah did.
Lots of sins are recorded in the Bible.
That does not mean it was ok. This was sinful action on Sarah’s and Abraham’s part.
God’s law is clear.