Splitter wont do the purpose..Splitter is used for combining signal from multiple satellites/lnb to feed into single receiver..The other way is wrong.
The two wires from dish are required for tata sky plus receiver if you want to watch a channel and record a different channel at same time since tata sky plus receiver is dual tuner ..
In your case if you want to use same dish for different settop box, buy a quad lnb which have 4 ports on lnb.. 2 ports can be used for tata sky plus set top box and remaining two you can use for another tata sky plus reciever or two set top boxes with single tuner.