Go to the black shark Facebook page and write on their wall, specifically mention that split screen feature is missing, even though it's available on the Chinese version and on most other phones. They will listen and pass this onto the devs, also ...
I must apologise for opening my mouth without checking properly! Even black shark said that split screen wasn't available, when infact it is. So I am sorry ! And thanks a million! After 2 months I've finally found split screen on the black shark 2...
I cant help you about the MHL adapter. Sorry.
Regarding Bluetooth devices. I use a BT keyboard, Microsoft BT mouse and a headset at the same time and it is working without any problems.