You can definitely include multiple sparkline widgets on the page. In the Widgetopia example included with the PDK, it shows you an example of using multiple sparklines on the same page. My guess however is that your problem lies in the value you are passing to the context attribute of the tag. If you have multiple sparklines on the page, you need to make sure each context attribute is unique to a particular sparkline. For example, you would do something similar to the following in your .jsp:
In regards to your second question, I don't quite understand what you are asking. Could you please rephrase the question?
For the second question, we are looking for some visual component showing x-asix in unit of minute/hour. the no idea how to do that in sparklineWidget or graphWidget. I understand the mouse hovering shows details (x/y asix info)
Can you post the error so I have a better idea of what the problem might be? If you are currently using FireFox, I recommend you install Firebug to help you debug. Firebug will usually help you narrow down errors that occur on your page. You can find it at http://getfirebug.com/