We had absolutely no clash in our house.
I was military (joined at 17). When I came home on leave, my parents treated me like every single ADULT guest they've ever had. Ditto when I brought friends home with me on leave.
My siblings (I have several) all went to college after highschool (I'm the oldest). Some lived away from home, some lived at home. Regardless... there were no more parent:child "rules". Those visiting were treated like every single ADULT guest my parents had. Those who lived at home followed the SAME rules my parents did.
A brief sum up:
- Everyone sets their own schedule. When the come and go, when they go to sleep and wake up, who they see where/when/and for how long they wish.
- It's polite to let people know when you're planning on being home for meals, but there is certainly no requirement to be home for meals.
- It's polite to let people know when you're heading out.
- It's polite to help with household chores (but there are no "assigned" chores) in addition to your personal living requirements, including offering to pick stuff up while one is out or on the way home from being out.
- It's polite to be quiet after others have gone to bed.
- It's polite to be inclusive / extend invitations AND
- It's polite NOT to demand or expect to be included / invited to all things and to give people their space
etc.
The only time I have ever seen a parent/adult child clash... is when parents are treating their adult children like children (as in an unequal relationship / parents having the "right" to be bossy and dismissive), or when adult children treat their parents in ways they would never treat any other adult that they're living with (ditto: an unequal relationship).