You can quick launch apps right into multi-window mode with Split-Screen Creator, an app that does just as the name implies, which is let you create a shortcut for opening up two apps of your choosing in multi-window mode with one simple tap. That said, there are a couple of caveats here that you'll want to know about if you plan to try the app out, which is free, but does also require an upgrade to pro if you want to unlock a couple of features - icon pack support and the ability to hide the launcher icon.
If you're asking yourself why you'd want to hide the launcher icon, it's because the app only really opens up to a settings screen. Accessing Split-Screen Creator is really done through widgets and there is a widget to take you to the settings screen so you can hide the launcher icon if you wish. To get started you'll need to add a widget to an open spot on any home screen page you have. Once you drag the widget to the home screen it will immediately open up the screen where you select which apps you want to create a shortcut for. This is where you'll come up against another caveat. While this does let you create multi-window shortcuts, it won't provide multi-window support for an app that doesn't already support it. This means to use the app shortcut, you'll still need to be picking two apps which already support multi-window by way of the developers adding this function in, so keep this in mind when picking your apps.
Other than that, things are pretty simple to use and there are no real hangups. You can even use the app to launch a multi-window mode shortcut for apps and device/system shortcuts. So if you want to create a split-screen setup of launching the Chrome app and a shortcut that takes you directly to a specific set of navigation directions in maps, then you can do that. Another thing to keep in mind is that this states it only works with supported launchers, but it isn't mentioned which launchers those are. Since the app is free though you can always test it and if it doesn't support your launcher then you can easily uninstall it and just use multi-window the standard way. It won't be as quick, but at least it will work. If you're interested in giving this a shot you can grab the app from the button just below, remembering that multi-window is a Nougat feature and you will need Android Nougat installed to use the app.