Sometimes I display 1 chart and sometimes 2, this is selected by the user. Is there a way to auto size the legends so that all items in the legend are displayed? The number of items in the legends will not be known until run time due to variations in the data.
unfortunately no, there is no way to auto-resize the legend.
one thing you might try, however, is setting the legend background color to transparent, then expanding it to a large size. this way, your legend items are unlikely to be clipped, and yet you won't see the legend box taking up too much space.
If I make the legend bigger it makes the actual graph such as the bars, pie, etc smaller. Is there a way to make the legend overlay the actual graph?
unfortunately no, unless you are using a composite chart, in which case the legend bounds are independent of the chart layer bounds.