You can set up a weekly code review where you take turns letting each developer present a piece of code they wrote to the team, and then discuss and give feedba

You can set up a weekly code review where you take turns letting each developer present a piece of code they wrote to the team, and then discuss and give feedback about that code. Also direct them towards resources where they can learn clean code practices. Perhaps institute a monthly "book club" where you select books about good coding practices. I would suggest starting with Clean Code by Robert Martin