so can thieves enter your house and steal your stuff? and if so is this why there are houscarls?

No...housecarls are just free followers. That eat your food and watch you sleep in their downtime.

good thing i use them to decorate hahaha i just wanted to be sure i didnt screw myself and have all my dragon masks taken

Thieves can go into your house and steal?

Looks like it's time to put up some fortifications. I will be needing a pet Clannfear to guard my place.