Actually… great point @Bastien_Siebman!!
@Joris, can you confirm your developers and clients are Guests of your Organization (as in they don’t share the same email domain than you)?
If so, here is something that might work:
Create two teams (Team A for your dev, Team B for your clients)
In Team A create project A and add your dev to this project
In Team B create project B and add your clients to this project
Multihome all tasks of Project A into Project B
As a result, your dev and clients will have access to the same tasks, but because they don’t belong to the same team or the same project, they won’t be able to see each other name, and will appear as private users.
Have a look at this other thread when users ended in this situation without trying to in the first place 
"Private user" for collaborators/Assignee - #5 by Bastien_Siebman