The project manager should ensure that the junior engineers make decisions within a certain responsibility level and commit to it1. This is because, in a project team, it’s important for all members, including junior engineers, to be able to make decisions within their responsibility level1. This not only helps in the smooth progress of the project but also aids in the professional growth of the junior engineers1. However, the project manager should also facilitate open communication within the team and provide necessary guidance and support to the junior engineers to help them make informed decisions2. References: 

https://pm.stackexchange.com/questions/26921/conflict-between-senior-and-junior-members