My kids aren't guests in my home, and now that they are married, their wives aren't, either. They both helped in appropriate ways a couple of weeks ago when both were here. DS #1 and his wife, often stayed here when they were dating and they had a commuter relationship. That situation was probably more like a guest thing, and she followed my son's lead. I don't have guests often, but I don't find it onerous. The only time I required anything more than clean up after yourself with my kids was last spring when DS #1 and his wife stayed here after going to a wedding near my house. As pre-arranged, we met them there at the end, DH took them back here, and I drove their car back here, as they had been drinking. DIL got sick in the night and tried cleaning up in the middle of the night. DH went into the bathroom and saw she had not done such a good job, which sent DIL into a frenzy of cleaning, as she felt horrible! I love cooking for others, and don't expect them to clean up, although they offer to help. We mostly go out, or take turns cooking and paying for restaurants.
My kids always write thank you notes to others, and perhaps having a Bar Mitzvah at age 13 and having to write 50-100 thank you notes seared it into their brain! The rule was to write 5 a night, until they were done. My older son ran for class secretary based on his thank you note writing skills! The class laughed at his speech. Two years ago, he single handedly planned and pulled off the ten yr. reunion. I told him it was payback for all the organizing I had to do for him. Seriously, give your kids more credit. I know some 18 year olds need more parental guidance than others, but if you do the talking and teaching along the way, it's not so bad.