To get the row you can dp:
GridViewRow gvr = (GridViewRow)((Control)e.CommandSource).NamingContainer;
and then to find the buttons and change their visibility:
Control buttonAprovar = gvr.FindControl("imbAprovar");
if (buttonAprovar != null)
{
buttonAprovar.Visible = false;
}
and the same for the second button.