Sharing cable (well running cables in closely in parallel) shouldn't be killing anything. Something else isn't right. And they shouldn't be just dieing for no apparent reason.

Without knowing the exact wiring, it's a bit hard to say what might be wrong but I'd guess more likely on the power supply side of things than anything

Wrong supply voltage?
Supply voltage connected somewhere it shouldn't be?
Missing power supply?
Correct voltage levels on the TX/RX?