I have recently gotten involed in an elementary school that has a PTO, a PAB (Parent Advisory Board) and a School Council. I am not sure if I understand the difference and or the need for all three. What is the difference and why do you need/want all three of these organizations?
Each should have its own mission, so you'd want to look at what those are and if there's any overlap. If there is, hopefully work together to define the differences so the groups fill different needs - or perhaps see if two can be merged.
Here, our PTO's are primarily responsible for:
Some fundraising (note, school also does fundraising)
Support of school activities
Each school also has a Campus Academic Advisory Committee (required by law, I believe) which is a formal committee of staff, parents, and community members that meet about 4 times per year and serve as a representative advisory group to the principal regarding strategic planning and policy decisions for the school. In our case there's no overlap between PTO and CAAC, which may be like your PAB.
"School Council" could mean anything. You'd have to let us know how it's defined in your school.