What’s the best way to divide the work between two freelance developers?

So I have a full-stack developer who has done everything up to this point and we need to speed things up a bit so I plan on hiring another full stack freelance developer.

I am unsure how I can divide the workflow, my current developer says that if I get another developer it may slow things down or complicate things.

I was wondering what would be the best way I can divide the work between two developers who are working remotely and the main developer have all the code. How will they both work together, like we aren’t using any cloud software to store our code or GitHub etc.

I am not very technical, any help would be greatly appreciated!