I think it would be best to get the full birth certificate, including your parent's names, translated from Portuguese into English, and indeed for that translation to be certified by the company doing that translation.
I say this not just because of a possible CoA application, but in due course the application for the spouse visa (which you will appreciate cannot be made inside the UK) .... but also because of various matters that might arise in the future .... applying for NI number .... taking out life insurance .... etc etc.