start with some mindfulness techniques. imagine a door at the front of your mind and one at the back. when the thoughts come in, they enter the back door and then instead of giving them power, just escort them out the back door. that is all the thought you give them. just keep on moving out the back door. since there is already a facilitator, talk to him/her about your fears. it is a mental health group after all, he/she will understand you being overwhelmed and the voices in your head. you dont have to hide what you are going thru. let the facilitator take the reigns and you join in until you feel comfortable. maybe you could introduce the principles of NAMI. that is simple enough. you would be taking part in cofacilitating. when the timer goes off, you could direct the meeting to the next person, that is simple enough. and maybe you could end the meeting and announce when the next meeting is. let the facilitator do the managing of the group and you jump in making comments when you feel comfortable until such a time when you feel you can handle more.