Fun box, I did not find it as easy as other people did especially with the enumeration, but here is what I can share.
Foothold
When life gives you parameters, mess with them. This will open a door that only privileged users can go through. Once through the door follows the path in front of you. Errors can reveal who you are and we all have flaws. Well-known exploit tools might even know about this flaw.
User 1
You favourite enumeration pod will reveal what should be of interest. Some keys can open more than one door. If you find such try it against all doors.
User 2
A collection of users usually have things in common. When we do thing we leave trails, they can be shrouded but with the right combination of tools and grep you can un-mask anything. You might want to find the interesting steps taken and then use the proper tool to look at those.
This is the best I can give without spoiling it for others
Root
If you made it to this point just gtfo here.
Thank @Dilan for narrowing my search for the second user.
PM for a nudge.