You can use a coaxial splitter with DECA adapters.
So 1 DECA adapter at the router, then use a coaxial splitter and 2 coaxial cables. One cable to the first adapter at HDTV 1 and another coaxial cable to the second adapter at HDTV 2. This setup requires only 3 DECA adapters and only uses 1 Ethernet port on the router. Read this thread below.