You want everybody reading and writing code in a standard way. There are two ways you can achieve this:
- Clone a single developer several times and make sure they all go through the same training. Hopefully they should all be able to write the same codebase.
- Give your existing developers explicit instruction on what you require. Tabs or spaces for indentation. Where braces sit. How to comment. Version-control commit guidelines.
The more you leave undefined, the higher the probability one of the developers will clash on style.