The content filter should be device-specific. So, I could play everything on my desktop, but filter songs on the old phone my son sometimes uses.
Somewhere on this website, Spotify claims "If you apply the setting on your phone, it doesn't filter explicit content for the same account on the desktop app." This is simply NOT true.
Updated on 2019-09-15
Thanks for submitting your idea to the Community :)
It's already possible to do this if you're both part of a Family plan. You can learn how to do this here.
Note that sharing Spotify accounts is not allowed, and hence we won't be able to accept your original idea.
More information about how the Spotify Idea Exchange works can be found here :)
Thanks! Stay awesome :)