Use a high quality satellite TV splitter, making sure it covers the frequencies you plan to use. My DirecTv splitter covers 2-2150 MHz. Adding a 2-way splitter will reduce each scanner by 2.5 DB. Since they use F connectors, you will need to replace the BNC on the coax with F, and make an F to BNC jumper cable to go from the splitter to the scanner. This would be the cheapest route. The one listed above, while more expensive, would eliminate the F to BNC conversions. Satellite splitters are 75 ohm, but it is doubtful the difference between 52 and 75 ohm will affect reception to any extent. Ive used them to split to two scanners in the house before, however, Ive never tried the one listed above.
DIRECTV SWS-2 Satellite 2-Way Wide Band MRV Compatible Splitter (2 -2150 MHz) from Solid Signal