Sadly this is keyboard-dependent. Most consumer keyboards only register a handful of buttons at once, except the modifier keys (shift, alt, etc) which always apply. It's hit or miss with how many (and which) register properly together though. :(

Thanks. After some search I managed to find test for keyboard ghosting, and it shows well some key combinations of arrow keys and space are incompatibe in my keyboard. However, using keys like C works just as well. I will just rebind Fire to X or V or something, I checked and X+C + any two arrow keys work all together for me

P.S. when rebinding, I saw default controls for players 2-4. I feel like this is not good decision in this case; not only it is uncomfortable for player 2 to have fire and ability keys between "up" (so have to basically hold one hand at top of other to be able to control fire/ability and movement at same time), but now that I looked at ghosting issue, it's clear that Q W E A S and D will hardly register together at more than 2 keys at once in row+line registering keyboard.
And if you add players 3-4 both issues are exaggerated - hands of one player will be uncomfortable for another (and it's not like people often buy more than one keyboard just in case they might all want to play on keyboard in local), and all of those controls are in two keyboard rows which means players' pressed keys will be blocking each other. I honestly not sure what could be done with this, aside maybe "players 3-4 might want separate keyboards" in-game warning or such.
And you can't rebind a key if it's already used in other player's config. Could it just allow user to disable keyboard players 3-4 altogether and setup it for just 2 players but in way that is more comfortable to control and less likely to suffer ghosting issues?

Interesting research, glad you found keys that do work in combination together. I agree the multiple keybinds on one keyboard are less than ideal (and perhaps the defaults are exacerbated by likely ghosting issues). Multiple players on one keyboard is already sort of "just for fun" because it's technically possible. 4 players on one keyboard is a whole different game in itself!