Sure about that, foxmoth?
You do need a Transport CofA (nowadays, the equivalent maintenance regime actually, but it's a bit of a grey area) to rent, but a Transport CofA plane can have a share group (a syndicate) around it comprising of any number of people. The 5% min shareholding is imposed on the Private CofA case.
Just having > 20 members does not make it a renting group.