The objective of using CToolBarCtrl::AddString to add multiple strings from a resource seems to be beyond what MFC is designed to accomplish with this function.
There are a couple of problems with this objective
1) The resource editor does not support separating multiple strings in a stringtable with \0 as a null character. If you manually edit a .rc file you can create the string resource with embedded nulls. However, subsequent usage of the resource editor will cause the manual edits to be lost. You can avoid this by creating your string resource in MFC's .rc2 file which is not used by the resource editor.
2) MFC's implementation of CToolBarCtrl::AddString uses CString to load the string resource. The string encapsulated by CString will not be double-null terminated.
You can use the workaround destribed in 1 above to create the desired array of null-terminated strings. As far as I know LoadString will not load a double null terminator from a resource but this can be worked around by using an adequately sized and initialized buffer to receive the string data. You can then use this buffer with CToolBarCtrl::AddStrings.