Answer to question #1 – According to 1×10, No. The other 2 genie lamps contained Cyrus’s brothers.
Answer to question #2 – According to 1×12, we got to see Amara again. She somehow turned back to a human from the snake staff. If her sons were genies for at least 100 years, then yes she must be immortal or at least have a gift of a very long live.
Answer to question #3 – According to 1×10, yes. They are Cyrus’s 2 brothers
Answer to question #4 – According to 1×10, No. The lamps came from Agrabah area where Cyrus and his brothers were cursed to become genies.
Answer to question #5 – According to 1×11, Cora taught RQ magic, much in the fashion Rumple taught Regina and Regina training Emma – to use anger and to start with fire.
Answer to question #8 – According to 1×12, Jafar did need Amara’s power to cast the spell to change the laws of magic, but he didn’t change her back. Not sure how she changed back to a human yet.
Nothing is impossible on OUAT. Everything has a way of repeating itself. Keeper of the Keeper tread: https://oncepodcast.com/forums/topic/official-keeper-thread-3/#post-217924