Currently, the first option is not possible. Considering the second one, the reason that you do not see a scroll bar for the inner grid is that the element in the row details is measured with infinity - that is why the grid takes all the space it needs. What you can try is to set the Width of the child grid or synchronize it with the one of the parent (an example for the latest approach can be found here).
All the best,
the Telerik team