You are great at fudging facts.
Sarah was DEAD when Abraham married Keturah.
You just ignore that silly little truth in order to spread your misinformation.
It was Sarah’s idea to have her maiden sleep with Abraham to produce and heir. Nowhere does it say it was from God.
Sarah was trying to ‘help’ God, she had lost faith that she would ever conceive. And we all know what has come of that ‘help’.
As for the rest, Sarai did no different than Rachael or Leah did just 2 generations later for Jacob (Israel). Perhaps their giving Bilhah and Zilpah respectively to Jacob was also against God's will? (that is now 4 wives from which sprang the 12 tribes of Israel)