Protecting the source code isn't trivial, since there are plenty of ways to get access to it, one way or the other, with the right motivation.

Step one is NDAs and non-competes, so that you can protect the IP if needed, in extreme cases.

Step two is hiring people with certain reputation. A lot of the good developers are involved with communities of some sort - related to the programming platform or something else. They maintain GitHub profiles and use other methods to be respectable in their niche. Those people are less likely to turn against you and perform shady activities, since their reputation can also be affected.

Step three is communication. Most of the internal conflicts happen due to the lack of proper communication - people getting rejected in a rude way, or not treated properly. Whatever happens over the months (years) can be communicated properly. Even if you part ways one day, it would be clear what the reason is, and it will be justifiable.

Most conflicts happen after a serious company drama that escalated with time, and with the right contract and attitude they could be prevented as well.