Abram, falling on his face with laughter. If its joyful laughter maybe that’s why Abram asked for provision for Ishmael too. Sarah laughs. If its a skeptical reading of God you would see them laughing at the promise. But if you read it as joy you can view it as Sarah and Abram accepting the promise and not caring about the why and the how. She could be concious of other people laughing at her because of her age (skeptical) or she maybe wanting people to laugh with her because of the absurderity of the promise of God (joyful)

Rivalry comes back because she sees Ishmael mocking. Sarah wants to protect Issac. God confirms to Abraham Sarah is right and to listen to her.

if you compare the story of Abraham and Adam theres some really common themes.

Man and God together, then woman does something that goes against the promise of the future from God (fruit from the tree/giving her slave as a wife) then theres a consequence (nakedness/Ishmael) then theres a rejection there wanting to hide or send away and then theres a completion of the original promise even if that looks differently.

God hears suffering and still says go back because he has already said there is blessing through suffering

Genesis 15:2 KJV[2] And Abram said, Lord GOD, what wilt thou give me, seeing I go childless, and the steward of my house is this Eliezer of Damascus?

Genesis 16:2 KJV[2] And Sarai said unto Abram, Behold now, the LORD hath restrained me from bearing: I pray thee, go in unto my maid; it may be that I may obtain children by her. And Abram hearkened to the voice of Sarai