I would suggest you let (sub-)apps know their real base not the parent's one, but you make the server responsible for climbing the path hierarchy to find higher level shared resources for missing local ones. This also makes it very easy to prototype new sub-apps, test changes to common pieces independently first, etc.
In a webserver like Apache, this would look like a rewrite rule (conditional on not finding a file) it just substitutes the same file in the parent hierarchy.
In laravel (according to the router docs) it looks like you can add optional 'directories' to your current rules, i.e.:
Route::get('/.../app/templates/{name}', function($name)
...
becomes:
Route::get('/.../app/{module?}/{item?}/templates/{name}', function($name, $module, $item)
...
You could then use $module and $item if you need to test a resource change with specific sub-app/items.
The drawback in making the server responsible for handling inheritance is the independent client fetch/cache of identical resources with different paths. But you can at least choose between large file inefficiency or access latency by using either rewrites or redirects. You can also always hardcode significant paths in production clients later and still benefit from having a hierarchy for testing and graceful handling of occasional errors in client side links.