To connect a Sky Q hub to your sling box and a TV at the same time you require an HDMI splitter and an HDMI/AV converter.
I bought this converter and it works a treat:- Musou® - | Full HD 720P/1080P Adapter | USB Charge: Amazon.co.uk: Electronics
I bought this splitter :- https://www.amazon.co.uk/gp/product/B01FSHZWIY/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1
At first it seemed to work perfectly, but I later found problems. When my Sky Q Hub was on standby the mini boxes worked, but when the Hub was taken out of standby the mini boxes reported a connectivity issue. The Sky Q Hub acts as a WiFi server which the mini boxes connect to and the splitter (which goes into action as the Hub comes out of standby) kills the WiFi signal. I hadn't noticed the problem when I first installed it because the Hub is connected to my router by ethernet. I moved the splitter 6 feet from the Hub but it still caused problems. I have resolved the issue by wrapping the splitter in a few layers of kitchen foil. Yay Heath Robinson is alive and kicking! I don't know if other splitters have the same issue.