Hi K.,
I have to be honest, while reading this, my first thought was they all need spankings when they do the behavior that you are not liking. But since you don't want to do that, I'm not sure the best method to deal with this. Basically, as you said, your kids are running your house and that is your job. You must change the situation or it will only get worse. Even if you don't do spankings, you must find another method of punishment, set the rules and then stick to them. Any and every time that they disobey the rules, they must deal with the consequences. I know it is hard. I am not very consistent with my own kids, but I do understand the importance of it.
Who watches the kids while you are gone? Whoever that is needs to be aware of the rules and make sure that the kids stick to them while you are gone as well. If it is Dad, then it would probably be a good idea to include him in the process of making the rules. My dh is excellent at getting the kids to obey. Sometimes kids listen better to Daddy for some reason.
There will always be some messes at this stage, kids are just kids. But the behavior you are describing is way beyond just normal kid's playing messes. I imagine you could probably find a book that would give you some ideas on discipline other than spankings. Here are some ideas that might work: If they get a snack by themselves without asking they do not get another snack that day. (If they get a second snack by themselves you will have to then think of some more extreme punishment) For screaming fits, I often send my daughter to her room. She is 5 and will often throw a fit when she gets in trouble. She goes straight to her room when this happens and usually a spanking as well. For the clothes issue, maybe you could make it as a rule that if they change clothes during the day without a good reason (maybe they have to check with you first) you will take away one of their outfits for a whole month and then stick to it and start taking away their favorite outfits. For writing on walls, make them wash them off, sometimes the act of having to clean up a mess is enough to get them to not do it again. We also have a rule in our house, that their is no computer or tv time if rooms are not clean. That is a big motivator as well.
Anyway, I hope this helps. It will probably require what seems like a whole lot of mean behavior on your part for awhile, but once they see that you will stick with the rules, things should get better.
M.