Afraid to say its probably just the start of miserable springs/summers . We are on our 9th year with at least one more to go after this, possibly 4. Oh to have a relaxed summer
As for using past papers for revision. Mine have always done them under exam conditions, marked them then written out model answers and then committed to memory any facts they didn't have or gone back to text book/notes for anything they didn't understand and done practice questions on that topic before doing another paper.
Simply copying out model answers would require a high level of concentration to actually learn it.
3 hours is certainly too long without a break. If they are studying then 10 mins in every hour would be my suggestion or after doing a paper.
A revision timetable is a good plan so as you say, time can be allocated to all subjects. Also so they and you can see when they should be working and when they can enjoy time off.