You need to create a custom control. For instance you could inherits from SimpleControl class.Then you need to create a control designer for your control. Your control designer should inherits from ControlDesigner class. In your control designer you should override LayoutTemplatePath and specify the path to your custom template for the designer basic tab. In this designer you should provide the ability for creating a new pages - respectively RadTabs. If you do not want these tabs to be a cms pages you need to create your custom data source which will be populated with the new data- persisting the tables.
Generally in the designer you should provide the ability for a user to select the page, then you need to get the id of this page and under it, create a new RadTab.
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