Add all your required validators to your mark up and enable/disable them in RowDataBound
this example use compare validator that validate a test value:
void Grd_RowDataBound(Object sender, GridViewRowEventArgs e)
{
if(e.Row.RowType == DataControlRowType.DataRow)
{
DataRowView rowView = (DataRowView)e.Row.DataItem;
String testValue = rowView["Test"];
CompareValidator cv1 = (CompareValidator)e.Row.FindControl("cv1); // checks between 2-7
CompareValidator cv2 = (CompareValidator)e.Row.FindControl("cv2);
cv1.Enabled = testValue.ToUpper().Equals("ABC");
cv2.Enabled = !cv1.Enabled;
}
}