(Ch.SeriesCollection(1) as Excel.Series).MarkerStyle = XlMarkerStyle.xlMarkerStyleSquare;
(Ch.SeriesCollection(1) as Excel.Series).MarkerSize = 8;
(Ch.SeriesCollection(1) as Excel.Series).Format.Fill.ForeColor.RGB = Color.FromArgb(0, 0, 255).ToArgb();
(Ch.SeriesCollection(1) as Excel.Series).Format.Line.ForeColor.ObjectThemeColor = Microsoft.Office.Core.MsoThemeColorIndex.msoThemeColorAccent2;
(Ch.SeriesCollection(1) as Excel.Series).Format.Line.ForeColor.Brightness = (float)-0.25;
(Ch.SeriesCollection(1) as Excel.Series).Format.Line.Visible = Microsoft.Office.Core.MsoTriState.msoTrue;

ActiveChart.SeriesCollection(1).Select
Selection.Format.Line.Visible = msoFalse ' вот тут выключил линию МЕЖДУ точками
Selection.Format.Line.Visible = msoFalse ' а вот тут выключил линию ВОКРУГ точками

                                (Ch.SeriesCollection(1) as Excel.Series).Format.Line.Weight = (float)1.25;
                                (Ch.SeriesCollection(1) as Excel.Series).Format.Line.Visible = Microsoft.Office.Core.MsoTriState.msoFalse;
                                (Ch.SeriesCollection(1) as Excel.Series).MarkerSize = 8;
                                (Ch.SeriesCollection(1) as Excel.Series).MarkerStyle = XlMarkerStyle.xlMarkerStyleSquare;
                                (Ch.SeriesCollection(1) as Excel.Series).MarkerBackgroundColor = Color.FromArgb(0, 0, 255).ToArgb();
                                (Ch.SeriesCollection(1) as Excel.Series).MarkerForegroundColor = Color.FromArgb(33, 55, 149).ToArgb();