OK I have now read this thread a bit more fully.
PRH I definitely disagree with you I'm afraid.
The 2012 Federation Regulations stipulate in Part 4, 21 (3) (a) "one parent governor elected or appointed in accordance with regulation 14 in respect of each school in the federation".
So in a federation of 3 schools you would have 3 parent governors at the moment (but OP you say you have 4?)
The 2016 amendment to the 2012 regulations states ' For regulation 21(3)(a) substitute— “(a) two parent governors;” and adds an explanatory note saying "Regulation 3 amends the Federations Regulations 2012 to provide that the governing body of every federation must include two parent governors, to be elected by parents of any federated
school or appointed by the governing body of the federation"
I think this does mean that if you have more than 2 PGs at the moment in a federation, you can only have 2 in future. What is not specified as far as I can see is how the 'surplus' ones will be dealt with. In the absence of any specific instruction, I'd say the existing ones can serve out their term of office but then they would not be replaced, leaving you with 2 PGs eventually.
Many federations only have 2 schools, therefore only have 2 PGs at the moment, which is more straightforward, and the only effect is that in future it is 2 across the whole federation, not one per school.
The reason I don't believe the stated numbers are minima is that if this is the case, the regulations will state 'at least'. So in the 2012 Constitution Regulations, 12 (3) (a) (which apply to maintained schools not in a federation), it says 'at least two parent governors' But for LA and staff it just says 'one'. Not 'at least'.
The emphasis of this government is indeed on skills as another poster has said. Parents can become co-opted governors if the GB is willing to appoint them in the belief they have the right skills.