Split View same app twice? Is it possible to view 2 apps at the same, eg. 2 × Mail, in Split View?
This is not possible in iOS 9. Only one instance of an app can run at any given time.

There is a small change in iOS 10 allowing two instances of Safari to run concurrently, but that is a special case. To do that, long-press a link, and select Open in Split View.