No they are not alive. They passed away and were buried in the cave.
Yes, we have narrations that when Imam Mahdi (a) appears, they will be resurrected by Allah and they will support the Imam.
Scholars have different opinions about where the cave is. Many believe it is in Jordan.
Some further readings on them:
https://www.al-islam.org/hayat-al-qulub-vol-1-allamah-muhammad-baqir-al-majlisi/account-people-cave-and-inscription
https://www.al-islam.org/enlightening-commentary-light-holy-quran-vol-9/section-2-companions-cave