Sorry for the delay to getting back to you.
We have analyzed your query and we implemented in following requirement in the attached sample.
1. Different Celltype in NestedGrid.
2. Implemented INotyfyPropertyChanged in Nested Grid for notify the underlying collection while changing the value from the grid.
3. Change the Nested ItemSource when click the button.
Please find the sample under the following location.
Please let us know if you have any queries.