..ehm I need to ask another question
I put my housecarl as my steward, but I want a separate housecarl and steward, because the more people the better, so can i for example kill my housecar/steward and get another housecarl to my house, and then appoint another steward?
No, that housecarl is permanently steward and housecarl at the same time. I recommend you load a prior save and get a follower other than your housecarl to be a steward.
Edit: Also, it's probably a good idea to save as often as possible when dealing with your hearthfire houses, in case you make a mistake.