According to the help screen, you're supposed to press the left mouse button and drag a rectangle over your squad to select them. This does nothing except tell me one of my members doesn't have enough action points. I'm in the very first sector and after the first little fight, I realized it's going to take forever if I have to move them all individually around the entire sector. I looked online and saw somewhere to try pressing =, and also shift + the spacebar but neither did anything.

Uhm, I'm not sure that you can actually move them all together in turn-based/combat mode. And even if you could then it wouldn't work very well since how far a merc can move in a turn will differ quite a lot from merc to merc. After the combat is finished though or all known enemies are killed the game will return to realtime mode and then you can drag-select everyone and move them around simultaneously without any issues.

I think there was a way, but not sure anymore....
shift + left click maybe?

And IIRC they only went as far as the slowest unit, but again not sure anymore.

Main reason why I never used it, those ambushes man, I tell you ;)