Do I have to download all of all at once, or I can just download each one at a time, because I have a low storage.
Install any single one, run the app, give it permissions, then run one of the remaining installers. Run the app again, let it finish. Run one of the remaining installers... Rinse, repeat, until you've done this for all five. Then, you're done.
For a more detailed explanation, read my guide here (which was adapted from my other post here).
Regarding low storage space: my guide has a section for that. You'll need enough to install the full game, plus space for one installer APK. If you can handle that (~8-9GB), you can install it. Otherwise, I'd suggest cleaning up your storage and making space, because this game is very much worth the trouble. Backup some junk to the cloud or your computer (if you have one). Or, just play it on PC, if you can—the experience is, quite honestly, much higher quality. Though, if Android is your only option, that is how I originally played the game and I enjoyed it very much.