1. Better use the number of days of the months and Sundays should be included in the calculation. You can of course 26, and compare. If it comes to the same amount, it should be OK.
2. 48 hours per week. Above that, will be overtime.
3. If he is required to work overtime, I think he should be paid, whatever his salary. If he is asked to work overtime and don't get paid, why should he work.