To achieve your requirements you will need to extract and customize the default ControlTemplate of the RadBreadcrumbBarItem. You can find more information on that matter in our Editing Control Templates article.
Once you extract the default ControlTemplate you will be able to find a RadSplitButton control named "SplitButton". You can change its DropDownPlacement property to achieve your second requirement. As for your first one, you will need to change the fixed size of the ScrollViewer that is defined in the DropDownContent of the "SplitButton".
For your convenience I extracted the ControlTemplate in the attached project (note that it uses our implicit styles). Please take a look at it and let us know if you need any further assistance.
Regards,
Pavel R. Pavlov
Telerik
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