In the A2b forms there are spaces for two people authorised to sign on behalf of the organisation. Only the first authorised person should be filled into the A2c form, and this is the signature you require – for the CPFs.
Then why have the space for two in the A2b form if only one is required for the A2c?
Well, you have to differentiate between the signature on the CPFs and the signature on the actual contract which will come later. The CPFs to not actually bind you to do anything, apart from saying that you are happy to be included in the preparation of the contract.
The contract, however, is different and legally binds the organisation. Some organisations require two signatures on legal contracts, so the A2b forms have a place for both. The Commission uses these two names in preparation of the contract.
When you receive the contract, it will quote both names and say that depending on the rules of the organisation they require either one or both of the signatures.