If participants are hearing (what sounds like) two audio streams playing at the same time, this is because audio from your workstation's speakers (i.e. Avid/Premiere Workstation, etc) is bleeding back into the live Evercast room via the microphone you are using to communicate inside the live room.
There are three primary ways to solve this issue:
1. Use a push-to-talk microphone: This will ensure that participants only hear you when you are speaking.
2. Wear headphones: If you wear headphones during a live session, you will not have any feedback issues.
3. Manual mute: When you are streaming content and not talking, manually mute yourself using the disable microphone button in Evercast.
If participants are hearing feedback, this is most likely caused by two people inside the Evercast room who are in the same location and are too close to each other. Either ask the participants to separate even further apart from each other, or one of the participants must mute their microphone and disable their speakers.