太空入侵者不能齐声移动（Javascript）

Firstly, I'm new to programming and Stackoverflow scares me, but I've tried to contain all the relevant code and to explain my problem well. I have seen many other posts regarding people attempting to make Space Invaders clones and even specifically the "invaders" not moving in unison. However, these posts have not solved my problem and I would be really grateful if someone could point out where I may have gone wrong.Firstly, I'm new to programming and Stackoverfl