My older ones remake their beds too. They're 9 & 12. DS is 6 & will attempt to remake his. I usually just do the fitted sheet for him.
Both younger ones also have a fitted plastic sheet on their beds, so I don't vac & don't need to clean their mattresses. I hate having to wash doona's though!
Through winter mine have sport commitments 3 days a week. But they still manage homework & chores. With down time. Sundays are big clean/washing days, but they're our only down days, so I try keep their stuff to a minimum. Get what we can done in the morning & the rest of the day is theirs.
It is tricky trying to keep the downtime just that!! THe girls have 3 nights a week for extra activities plus the 12 year old is doing her grade exams for flute and violin so needs to do at least an hour of music per day as well. I am trying to find a good balance for all of us, but am thinking sheets on Sundays will be a good place to start, they can do the sheets while I make pancakes!!