Limited permission Rights

[Deleted user]

How can I limit the access to certain elements like due dates or changing the project milestones for other people?

Or how can I add an approval before anybody tries to change the deadline of a task?

[Tayyab Bashir]

Editing and viewing due date is only allowed to people who have schedule issue permissions. 
So you can go to your permission scheme and see which user roles/groups have that permissions. 
You can then add/remove people from that group you want. 

And similarly you can explore other project related permissions over there as well. 

shortcut: g+g --> Permission Schemes