Sorry, I tried to bring a quote from the February 6, 2016 session, page 23, by "Miss T", but my little android just locked up. Any way, there was a section about toning using vowels in there that struck a chord with me.
A couple of years ago my ex and I went into an art gallery in Combs, BC. There was an elderly Scottish lady looking after the shop. She asked me to tone with her. I wasn't sure what to do so my ex wife started us off with an Eeeeeee. We picked up the tone and carried it for quite some time. My ex, Sandra, quit after a short time but we carried on. Our voices began to modulate with vibrato. It was quite a spiritual experience. Sandra said that it was the most beautiful sound she had ever heard, like a whole choir of Angels.
Don't get me wrong as I am a karaoke king. Quite often when I sing, I go into what I call a dream walk where I seem to be living in the song. I always get ovations when I sing in public and I go to that place. I can never seem to be able to get through Puff the Magic Dragon without breaking into tears, however!
Not everyone is good at singing songs without lots of practice. Possibly by starting simple using a tone as a group, where it would be easier for the group to find harmony, might be a good place to start.