Overall/Read does not give them access to any project (just Jenkins itself). So give the demo user 'Overall/Read' globally, as well as 'Job/Read' (or just 'Read') for the specific projects. Do not give them 'Job/Read' globally.
The only thing missing is that they don't automatically have access to newly created projects, which seems a very unusual requirement (and surprising to your users?). You can use Create Project Advanced Plugin to give config access to a newly created project to its creator if that's what you need.
Alternatively, you could give them 'Job/Read' globally, and then configure the projects to not inherit permissions from their parent (added in a recent plugin version IIRC). But that's likely going to be rather annoying and error-prone.
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