Not a pilot, but I'll give you it from a technical side.
Not all 747's are the same, RR powered a/c have 2 bottles per engine, so rotating left then right will fire 2 bottles on the same engine.
GE and PW powered a/c have 2 bottles per wing. So if you rotate handle left then right you will fire the 2 bottles into that engine. None left for the other engine on that wing.
If you rotate 1 handle left and 1 handle right then 1 bottle is fire into each engine, that way ensuring each engine has a fire bottle dispensed into them.