Uhhh, you need to brush up on your vampires. If we were to take Bram's Dracula as the default vampire, he can transform into a bat, wolf, and mist (there may be others, but I forgot). All this says, he can transform into dark thing. He could transform into a spider likely.
Also, there have yet to be vampires that transform into anything in TES. The only mention of transformation is a type in Black Marsh that can become fog.
Incorrect. It is Valenwood's Keerilth who turn into mist. They are the only known vampires for transforming into something. I know vampires in ES have different varities. Over one hundred clans exist in Tamriel, we only know a few of them and their powers.
But vampires (if thats what you mean) are not half bats. They have as much in common with bats as with mosquitoes. Werewolves are half men, half wolves. At least that's what I understand from the lore.
Yes, but do not compare werewolves with normal wolves. They do have a a Beast inside that hungers for blood and flesh. But that does not mean werewolves live as much as normal wolves. They aren't even considered natural by "normal" standards in the Elder Scrolls universe. They are not just half men, half wolves. They are men and women with a Curse that turns them into wolves. Yet they retain some of their humanity. But they suffer from insanity and violence and mental issues. I think werewolves have prolonged lives rather than a decreased lifespan.