You can kill several people in the guild, but there are some that are quest-related and are set to Essential, so you can only knock them out. It wouldn't be entirely realistic to kill an entire guild anyway.
You can sort of steal someone's house, but all of the containers inside aren't safe, so they will reset the items inside, meaning anything you put in a container will be lost. The bed (and sometimes other furniture) will not belong to you, so you won't be able to use it. But you will be able to come and go as you please and drop your loot inside the house without any problems.
But, of course, if you're on PC, there are ways to solve both of those problems.