I teach and have had four of my children in the same school as me at various times, including teaching them.
I don't mind teaching them when they are younger, but as they get into GCSE courses there are more hours per subject and that tips the balance. If my elder DD's were in school with me, I'd teach them about 20% of their timetable, as well as being their housemistress and doing duties.
I find that when they are in the same school, they rely on you for replacement letters, tuck money, and anything that other kids would have to plan ahead for. They also never have to deal with public transport.
I think it is great to be in the same school when your children definitely rely on you, but when they should be getting more independent, it is a good idea to be in different schools.
As a school business manager, it really depends on the financial situation of the school. If you have to make difficult decisions that impacts on the comforts of the students (along the lines of no colour printing, or reduce canteen choices, for example), it is possible that your child could take some flack, but unlikely.