Originally Posted by
Bus Driver Man
Only dual cooling/cranking. The actual start is still one by one.
(On the A380, 2 engines are started simultaneously. But the APU is more powerful to be able to do that. No idea about the A340 and B747.)
One the 747-400 (with autostart) and the 747-8 you can start two engines at a time - although if you're at higher altitudes you probably don't want to.