Issues with External monitors and devices

I've been having a very frustrating time as of late with external devices, more in particular, monitors.

95% of the time my 3rd monitor does not work. I have a 27" LG monitor hooked up to a DVI adapter, and a 24" Philips monitor hooked up to a DVI adapter with a DVI to HDMI cable.

iMac is a late 2013 27" model, pretty maxed out on everything.

Most of the time my LG monitor works fine, my phillips monitor mostly does not work and gives me the flashing black screens on the other displays like its trying to connect it but it continuously flashes until I unplug the cable.

Lately I've been having issues where all external monitors stop working and the only way to get the LG working again is to do a combination of switching the thunderbolt port and restarting the computer. The issue is sometimes when I restart the computer my Wired keyboard stops working and I have to re-start again.

I also then get the occasional issue of Video/Audio not playing on all platforms (Spotify, iTunes, YouTube, etc)

All-in-all this has been very frustrating. I just would like all three monitors to work without a hitch. The last time they all worked together was when I had Mavericks.

Any ideas on solutions?