Avoid if possible, is the easiest answer. Encourage your colleagues to move their code into proper packages when they're happy with it, and restrict notebooks to _use_ of their code.

Failing that, I think fast.ai's nbdev[0] is probably the most persuasive attempt at making notebooks a useable platform for library/application development. Netflix also has reported[1] substantial investment in notebooks as a development platform, and open-sourced many/most of their tools.

[0]: https://nbdev.fast.ai [1]: https://netflixtechblog.com/notebook-innovation-591ee3221233