You can't without mods.
You can acquire the Skeleton Key through the console command player.additem 0003a070 1. Source: Elder Scrolls Wiki page "Skeleton Key (Skyrim)"
Skyrim for Pimps - 2011 Quest for the Skeleton Horse 3-5 was released on: USA: 24 August 2012
0003a070
Yes, there are werewolves in Skyrim, and the player is able to become one.
There are no classes in Skyrim, a character is free to develop and become proficient in whichever skills they wish.
You can't but you can get the Skeleton Key as part of Thieves Guild quests which is a unbreakable lockpick!
I don't believe you can summon a skeleton out of thin air like an atronach or familiar, but if there is a dead skeleton, you can use the Raise Zombie or Reanimate Corpse spells, and it will revive and fight for you.
You cannot become a Werebear in Skyrim, unless you've added a mod that gives you that option. The only were-creature the base game offers, is Werewolf.
No.
You have to buy the DLC
No. When you have completed the quests, there is no way of getting it back!
sometimes you can turn into a skeleton by eating something