need to update quantity automatic when I combine two items using BOM

 have item A and Item BI have Qty of item A is 11
I have qty of item B is 10

Using bill of material I need to combine Item A and Item B into one itemAB
once I combine both I need to have in stock automatic without miscellaneous receipt an dissue
qty
Item AB= 10
Item A= 1
Item B= 0

I sold 2 item of AB
later I need to de-combine AB into Item A and Item B
I need to have in stock as qty
Item AB = 0
ItemA = 9
Item B = 8