Sometimes I just want to spare them the chore when they have had a busy week.
By the time they get off the bus, have snack, and do homework, it's almost dinner time. Then they have such a short time to unwind or play before bed. If we have to go somewhere on a week night it literally takes up all their free time.
Part of me thinks I should never do this, but about once a week I straighten up for them because I'm here and they are "working" at school. I think their creative time is so important and sometimes I just can't see ordering them around when they need to be free after a day of structure. Is this spoiling?
I don't think it's spoiling them, unless they start to expect you to do it, believe it isn't their responsibility at all anymore and don't appreciate your help. I think it's fine for family members to help each other with chores. If it seems like they are regularly relying on you to clean up, perhaps you can work together for a quick 10 or 15 minute tidying, just to reinforce that it's still their job.
My kids clean up their own rooms. But I don't make them do it everyday, it's a once a week thing so we can clean. I do make my 4 year old's bed sometimes if he asks and I usually put away some of their clean clothes so I can straighten up the drawers but that's about it.
I don't think it's spoiling them if you help them clean up once in a while.