where you are trying to chart two separate things: entry and exit, you will need to use two combined charts (using 2 while loops).
the line chart does not offer an option to remove the line connecting each point together, this is a limitation of the chart type.
One thing that may help is to use two different chart types,
Create the entry chart as a bar chart and the exit chart as a line chart, see the "Creating combined charts with the XML Editor" tutorial in the solution recipe section of the Dynamic Web Charts support page:
The dot markers cannot use an external image to change them, they are fixed in the flash object.