Currently, the categorical charts (bar, line, and dot) are able to use only one URL column per graph. However, if I interpret your intent correctly, you should be able to combine your three URL columns into the same column and reference that column from all three bar chart statements. Let me know if that works for you.
Remember that when you post code to the forum anything related to HTML tags can throw off the posting mechanism and truncate your post (anything meaning < and > symbols -- which are also part of HTML tags).
Using < for < and > for > as well as how to use se the [pre] and [/pre] tags around your code and output in order to maintain indenting and spacing.
It's not clear to me what's up with your bars -- are you overlaying the bars or having them side-by-side? It seems as though the last URL is the one used -- which is what I would expect if you were overlaying the bars, one on top of the other.
Note that I let gchart draw the first bar (back-most bar), and then I annotate the overlapping bars. You can control the charttip/drilldowns of the gchart bars using gchart vbar's html= option, and the charttip/drilldowns of the overlapping annotated bars using the 'html' variable in the annotate data set.