get another key cut.
shut the boys' doors and do not do in - to be honest, you shouldn't really anyway, especially the 18-year-old - he's an adult, I think you said paying rent, so he should not have anyone entering his room without his permission.
Your priorities are a bit skewed, that's all - having boys turn into men who have never had to lift a finger is a bad thing to anyone and everyone. An unmade bed is only a bad thing to you, and as it's not your bed it's actually not your business.
The thing is, if they know you will go in and make the beds, of course they will never do it, or always make sure they do it so badly you do it for them. Same with cooking, same with getting up and out, same with everything.
What if you decided this Saturday that you had a load of things you wanted to do and went out and did them - would a nice meal be on the table at dinner time, just as you would have made if you'd been home? If the answer is no, and especially if the answer is no because none of them (DH included) was prepared to give up their day's, or afternoon's, activities, then you are living with 3 very selfish men. Very.