Safe is a multi-platform license. You can add or removed device using My F-Secure online portal. The Internet Security version is usually cheaper and is not multi-platform. Protection wise, I believe there is no difference.
The antivirus is a extra stripped down product without for example any family rules feature/option. F-Secure more or less phased out the antivirus version in favor for what they nowadays call SAFE. Even if it's possible to find a download for the antivirus on their official site, new customers can't buy it.
Anti-Virus can no longer be bought by new customers. Instead, you’ll get the much more advanced F‑Secure SAFE. It provides the same advanced protection with extra security for online banking and shopping. It also extends the protection to cover your smartphone and tablet.
The latest stable version for F-Secure on PC have been updated to 18.0. The update should happen automatic. Otherwise please test the " Search for updates " option. Update information also found in the local UpgradeMessages folder. At the moment their change/release log page hasn't been posted...