I prepared a sample for you. I used a collection of buttons to attach same context menu to 3 buttons. I did not use Rectangles as they can't have child. You cannot have Big rectangle with small rectangles in it . I have attached 1 context menu to the UserControl so you can click anywhere in the yellow area and you will get a context menu. And there are 3 buttons on the page. When you right click on them you will get different context menu.
Please take a look at the attached project and tell me if you need more help.
p.s. Please remember to set Windowless="true"
for your Silverlight page, it is set in the .aspx page of your Web project.
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