In order to be able to copy sheets, without changing the active document name, you cannot proceed as you tried. It will always save the sheet, but the workbook will be Saved As your last allocated (csv) name.
Try this code, please:
Sub testSaveSheetAsCSV()
Dim import_bt As Worksheet, import_brd As Worksheet, wb As Workbook
'I used dummy sheets name only for testing reason. Please, use your real ones:
Set import_bt = Sheets("Test") 'use here your necessary sheet
Set import_brd = Sheets("Teste") 'use here your necessary sheet
Set wb = Workbooks.aDD
import_bt.Copy Before:=wb.Worksheets(1)
wb.SaveAs fileName:=ThisWorkbook.path & "\import_bt.csv", FileFormat:=xlCSV, CreateBackup:=False, Local:=False
import_brd.Copy Before:=wb.Worksheets(1) 'it will save its first sheet
wb.SaveAs fileName:=ThisWorkbook.path & "\import_brd.csv", FileFormat:=xlCSV, CreateBackup:=False, Local:=True
wb.Close False
End Sub
It adds a new workbook, copy the sheet necessary to be transformed in CSV, before the existing first one of the newly created workbook and save it (AS CSV) after that. It repeats the steps for the second sheet and closes the temporary workbook.
If you need to avoid the warning regarding overwriting of the existing file(s) (if the case), the code can be adapted to avoid it. Only in case you want playing with the code, or updating the existing csv files with the last necessary ones.