[ryanier]

Con la ayuda de AgustinOrtu y otros colegas el código lo implemente de la siguiente forma

Código Delphi [-]
procedure TFormMain.MostrarForm(FormClass: TFormClass; Owner: TComponent; Parent: TWinControl);
var
  Form: TForm;
  i: Integer;
begin
  for i := 0 to Parent.ControlCount - 1 do
    TForm(Parent.Controls[i]).Release;
  Form := FormClass.Create(Owner);
  Form.Parent := Parent;
  Form.BorderIcons := BorderIcons - [biSystemMenu, biMinimize, biMaximize, biHelp];
  Form.Align := alClient;
  Form.Show;
end;