Actually, I kind of had to deal with this with BodyFlow, when I took on a time-slot that was brand new for that class at my gym (Mon. 6:15 a.m.!). For a few months, we had two or three people, and like you noticed, people don't really want to be the only two or three people every week.
So you really have to be the one to build the sense of group, of community. I learned by trial and error what worked. Asking the GFM to put up a flier on the door that sold the class for a few weeks. And with the few extra people who showed up, treating them like they'd already been coming every week.
In a small group that's just forming, the element of connection is more important than ever. Work it! Make them feel that special sense of community and doing something special that gets us hooked on any class we love. Make them laugh! Reinforce that sense of team, of belonging, of a mission of fitness. Make a point of saying, "See you next week," "Please come back," any of those things that make people feel like they will be missed if they don't come. It's a tricky balance, between seeming like you are desperate for someone to come, and that you look forward to them coming.
Build your classes one person at a time; find out what each person likes about the class, and reinforce it every chance you get. Befriend your class - I don't teach BodyVive, but I look forward to teaching it, because I think it has the chance to build that friendship built into it better than any of the other formats.
Most importantly, decide why this class is special to you, and live it, breathe it! Your excitement about the program is contagious. I can feel your doubt just by reading your posts, so you've got to know your members will feel it, too! Figure out why you love BodyVive, and if you don't feel that passion already, what parts of it you do love, and focus on them.
Um, didn't mean that to turn into a lecture. But I can tell that there's a lot of worry in establishing this program, and worry that it's not going to be successful. Each of us, as instructors, are the only people who have the potential to make it successful! I would imagine that each Les Mills program has gone through that process, finding its audience, its identity. It's up to us to take on the call, to spread the program, to take what we love about it and share it, and to let the program directors know what can be improved.
I'm really excited to see how BodyVive grows!