What exactly are you trying do combine... Foxtel and terrestrial?
From your description, your best solution would be to transcode the satellite receivers (AV... HDMI is best) into DVB-T, then using channel amps to balance all levels prior to the distribution amps.
This is the basic method of SATV/MATV signal distribution systems.
If you are distributing RF to ordinary TV's, it's false economy using analogue modulation, given that most manufacturers are ceasing building TV's with analogue tuners.
You need to provide a distribution system design plan, noted with signal measurements at various distribution points etc.
It's a complex balancing act and there's no single answer, without knowing specifics.
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