Delphi – Firebird error “username and password are not defined” with Delphi application

Database password for access databases is not related with user level access rights, it is used for encrypting the database.

You can indicate the database password in the connection string with Database Password=mypass for Jet/ACE OLE DB or Pwd=mypass for OLE DB for ODBC or set it in the last page of the connection builder.

Embedded can't be used by multiple users at the same time (even if it's two applications on the same machine). See here for information on the differences between the three versions. There's also information in another SO question that might help.

As far as specifying a server at runtime, this may help:

procedure TForm1.Button1Click(Sender: TObject);
var 
 Conn: TSQLConnection;
begin
  Conn := TSQLConnection.Create(Self);
  try
    Conn.DriverName := 'FirebirdConnection';
    Conn.Params.Add('User_Name=SYSDBA');
    Conn.Params.Add('Password=masterkey');

    // Replace the dbname in the next line with the
    // value obtained at runtime, as  in
    // Conn.Params.Add('Database=' + YourNewPathAndDBName);
    Conn.Params.Add('Database=C:\FireBirdData\YourDB.fdb');

    Conn.Open;
    if Conn.Connected then
      ShowMessage('Connection successfully made to DB');
  finally
    Conn.Free;
  end;
end;