You have a number of issues that you have to get past.
First if we look at the simple case of I have 2 cheap USB web cams. You first have to solve the software issue of how you get both active. Some software can support multiple, some software you can launch it multiple times and select the camera and port to stream on and some is stupid and only do a single camera.
Now with a camcorder you first have to have a way to get the data out of the camcorder and into the PC. Many times you need a special capture board to do this. And if you want to run multiple you have multiple boards or a board with multiple inputs. Some new camcorders can run on USB but you still have the software issue.
You best bet it to look into cctv security products. They have solved most the how to hook it up problems but you would still have to find one that could broadcast itself or be computable with your broadcast software.
I have been unsuccessful trying to find answers to this. I broadcast live music bands with a webcam, I want to move up to a higher quality camcorder and want to add 2, 3, maybe 4 cameras for the same stream and switch between them. Do I need a hardware interface or a software interface to connect and switch between cameras? Both for Mac and PC.