Germans act in alphabetical order at the same advantage level, right?
Yes. Americans act in any order you want to (at the same level).
Also remember there can be some interruptions to the normal order. Someone can be given a command by a commander (which may result in that someone now suddenly being on a row above everyone else, so he must take an action) or someone helping out firing a machinegun (which can be done even if one of the two is on a lower row).