You can't plug monitors into both cards if you have CrossFire enabled.
Is crossfire enabled? Also, for the R9 260x you will need a displayport hub in order to use the 4th monitor. You can do DVI + DVI + HDMI or you can do DVI + DVI + DP or DVI + HDMI + DP. In order to use 4 monitors you need a DP hub to do DP DP DVI DVI or DP DP DVI HDMI.