infrequentflyer789,
Everyone on the flight has already been declared dead by an official accident investigation. Even if that isn't recognised in Brazil, then there will be jurisdictions where it is, and AF & AB have a lot of presence around the world - plenty of places to sue them.
This is not so straightforward. Some brazilian relatives already tried to sue Airbus in the USA, but the american judges
refused that (link in portuguese). Besides, I think each jurisdiction is sovereign to accept or not accept the "official declaration" by BEA.
There is also a juridical thesis affirming that as most brazilians victims bought their tickets in Brazil, AF and AB must be sued under brazilian legislation. And here, if you can´t have a death certificate derived from the identification of a body, you must have a "presumed death certificate", that is a considerably longer and bureaucratic procedure.
PS: I´m not a victims´ relative.