jsnone1 Why not get a TM751 to experiment with? It will take the RF from the sensors and place it on the power line!
Yes there are better transceivers out there but this is the cheepest to experiment with!
You can place it as close to the sensors as needed (provided there is an outlet there)!
House construction varies so much that even foil backed insulation will stop RF signals from getting to your desired location!
A repeater may not be your best solution (depending on location of your sensors)!