Accessing British Embassy in Brasilia

British embassies all over the world are there to assist British nationals with their needs, but .....

My personal experience has been poor, finding them far from reasonably priced and they come over as a commercial operation rather than an establishment (in part) dedicated to assisting British citizens abroad. Appointments tend to be hard work and you have to wait too long but, when you finally get there, you're the only person in the place.
You have to hammer at them and insist on an appointment if you want to get anywhere or they just fob you off.

Many things Embassy cannot do. I had to do the background check in US. All docs had to be translated and apostles' in US (via on line company). Birth Cert via state record where born.
Do not know which documents you refer. BR consulate has a check list and maybe some companies in UK can do the legalize on line. (Does take some FedEx type companies back and forth to UK). There are translation companies there Brasília. Maybe Interpol for background checks.
PF helped me a lot.