It depends on the lore or mythology you're referring to. In many stories, shapeshifters are not immortal but have the ability to change their form. However, there are also versions where shapeshifters can live longer lives or have a form of immortality.
It depends but most of them are not.
Werewolves are shapeshifters
Bruce Coville's Shapeshifters was created in 1999.
weightlifters
There are several shapeshifters in X-Men, but perhaps the best known is Mystique.
Yes. Shapeshifters are polymorphic because they can change into any form they want to.
Shapeshifters and werewolves ;)
Just one: Beorn.
Yes, because shapeshifters are werewolves
Vampires and werewolves/shapeshifters.
Shapeshifters - Helter Skelter Lyrics
Yes. Many cultures have myths about shapeshifters.
The Nightworld series is a very good series about vampires, werewolves, & shapeshifters falling in love with humans. There are 4. Vampire Academy series and The Vampire Diaries.