I presume you have what is called SLX active splitters on both decoders. Next I presume you are happy that the remote TVs away from the decoders will only be able to get SD quality?
IF HD quality is required, you will have to use HDMI extenders, and the best people to approach are
www.hdcabling.co.za
If happy with RF then, you have a few options:
Option 1:
Make sure the RF OUT of the one Explora is connected to the RF IN on the other ( this is the HB cable).
Tune all the Tvs connected to the second decoder to a different UHF channel number and then all TVs connected to the second decoder will be able to tune in to both decoders. This leaves the TVs currently connected to the first decoder out on a limb.
The only way to fix this is to remove the TVs connected to first decoder from the RF feed and move those TVs to be fed from the second decoder. Take the RF OUT signal via a simple T-piece, to the SLX splitter for each group and job will be done.
Option 2
Controlling the decoders from all these remote Tvs is not going to work very well.
The ONLY way to resolve the control issue is to change the RF connections completely.
Connect the two decoders together RF IN - RF IN for the HB cable
Take the RF OUT signals from both decoders via a T -piece, then to the existing SLX splitters. This will ensure after setting all to two different UHF channels, numbers that remote control of both decoders will be possible with the correct settings on both decoders.
Send me a PM if you want more help with the settings. but then please let me know what "splitters" you have for distributing RF at the moment.