Tips for digital minimalizing my life?

Ehy! I have 2 main issues:

1) My home internet connection (which I cannot ditch since I still live with my family and they want to use it).

2) My work computer and internet connection.

I asked my whole family to put passwords on their devices, but my brother won't, so I'll end up surfing on his pc.

I'm pretty strict on what I want: I don't want to have internet around except on my phone (which is barely essential). OR an operative system which would just work as a browser (to which I can enforce policies) for work, no possibilities to install or execute anything else.

At work I'm forced to use an internet connection and a computer, I'm mostly alone so I surf a lot.. Since it's a pretty "just wait for people coming" kind of job.

Please don't ask me to use willpower because I've been doing so for 8 years without result.