1) Be firm but in control. Do not scream or yell, or even nag. Just say what you mean, mean what you say, but don't be mean with how you say it. I know that sounds cliché', but it is an effective way to communicate.
2) Make out a list of what you expect each of them to do. If you can narrow it to 2-3 expectations, you are better off. Put it in writing and be very clear.
3) Make a list of consequences for if they don't follow through. A small consequence for a small infraction. Ex: If you fail to take out the trash, you lose game privileges for a day. Larger infractions lead to greater consequences. .Ex: Disrespect results in home confinement for a week or two or three. There needs to be some sort of extreme consequence for total disrespect. All of these will be different for each child.
4) The flip side is a basic reward system, made up the exact opposite of the negative. A small reward for taking out the trash for a few days. A larger reward for a good week or so. A significant event for the family if all of them do well for say six weeks. This can be difficult with the wide ages and interests, but surely they can agree to something.
5) As much as possible, let them help you draw up the contract. Let it be theirs. In the process of doing that, ask them what they might like to see you do different, This is only fair. Maybe spend more quality time with them. Dont yell, etc. It is usually nothing major.
6) On the matter of the clothes, if they can't put them up, don't clean them. Let them do without. they are big boys , They can clean their own clothes.
7) Make it very clear to the 18 year old you are not bailing him out when it comes to college time. He is expecting you to.