This is not supported by RadGridView as only one cell may have the focus , be in edit mode and trigger the editing events as described in the docs.
A descent hack would be to replace the TextBoxes with TextBlocks in the cell template. This means to use the CellTemplate property of the column and assign it to a data template containing a TextBox bound to the relevant property of your business object two way.
In case you decide to go that direction let me know so I can assist you further.
the Telerik team
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