Both Elite Dangerous and the Horizons expansion can be shared between all PSN accounts on the console that you've set as your Primary PlayStation®4.
All in-game extras such as ship kits, paint jobs, flight suits, etc. are unique to your PSN account and are not shared to other PSN accounts.
For help on setting a specific console as your PSN account's primary console, please see this guide from Sony. Remember that it is only possible to deactivate a console as your Primary PS4™ once every 6 months.