Example of parallel Mongoose execution.

gistfile1.js

var performers;

performers = {};

async.parallel({
  conductor: function(callback) {
    return conductor.find({}, function(err, result) {
      return callback(err, result);
    });
  },
  soloist: function(callback) {
    return soloist.find({}, function(err, result) {
      return callback(err, result);
    });
  },
  orchestra: function(callback) {
    return orchestra.find({}, function(err, result) {
      return callback(err, result);
    });
  },
  chamber: function(callback) {
    return chamber.find({}, function(err, result) {
      return callback(err, result);
    });
  }
}, function(err, performers) {
  return res.json(performers);
});

If you're not going to do any processing on the result from mongoose, then there's no need to setup your own callback, just pass the async callback in to the find method, eg:

...
conductor: function(callback) {
  return conductor.find({}, callback)
}
...