I have a new video card "http://www.bestbuy.com/site/pny-nvidia-geforce-gtx-950-2gb-gddr5-pci-express-3-0-graphics-card-black-blue/4457400.p?id=1219750645693&skuId=4457400" placed into my gaming build that I had updated too a more modern cpu and board.  I have one MONITOR connected too a vga kmv so that I could switch between the two and another on a dvi switch too do the same.  I used the vga to dvi converter but, when I boot windows doesn't show on that screen or detect the display.  What happens when you connect the monitor's to the card directly, ignoring the KVM switches?it works but, I have too have it connected to that kvmSo if I turn on the other computer connected too the kvm it will display on both Back again.
 Ignore this Post.
The hardware approach deals with switching the video feed of two SOURCES.
Hardware can be pricey.
The software APPROACHES is if the sources are from web sites. Perhaps somebody else here can show you how it is done in HTML code. Maybe for free.

Rather than provide a place to buy hardware. I would instead recommend a book on the SUBJECT. Some video monitor equipment gets to be expensive.  You can get a helpful book used from Amazon and get it delivered in a few days. Expect to get a good book on the subject for under $20 used.
Closed Circuit TV Surveillance GUIDES(From Amazon.)
That is the best I can do for now.   What?  I had too have the keyboard and mouse cables connected and now it is showing