procedure SetEnabledAll(Control: TWinControl; AEnabled: Boolean);
var
  c: TControl;
  i: Integer;
begin
  Control.Enabled := AEnabled;
  for i := 0 to Control.ControlCount-1 do
  begin
    c := Control.Controls[i];
    if c is TWinControl then
      SetEnabledAll(TWinControl(c), AEnabled)
    else
      c.Enabled := AEnabled
  end;
end;

SetEnabledAll(RadioGroup1, not RadioGroup1.Enabled);