Refactoring a nodejs function

fellows.js

var peers = function(req, res) {
    var peers = [];
    models.Fellow
    .findById(req.params.id)
    .then(function(fellow) {
      if (fellow) {
        switch (fellow.level) {
          case 'D0A - MONTH ONE':
          case 'D0B - SIMULATIONS':
          case 'D0C - SIMULATIONS':
            fetchTeamAndCohortPeers(req, res, fellow, peers);
            break;
          case 'D1 Jr Consultant':
          case 'D2 Consultant':
          case 'D3 Consultant':
          case 'D4 Consultant':
            fetchPeers(req, res, fellow, peers);
            break;
          default:
        }
      } else {
        res.status(404).json({
          message: 'Fellow does not exist'
        });
      }
    })
    .catch(function(err) {
      logger.error(err);
      res.status(500).json(err);
    });
  }
};

var fetchTeamAndCohortPeers = function(req, res, fellow, peers) {
  models.Team
  .findById(fellow.team_id, {
    include: [ models.Fellow ]
  })
  .then(function(team) {
    if (team) {
      _.each(team.Fellows, function(peer) {
        if (peer.uid !== fellow.uid) {
          peers.push(peer);
        }
      })
      fetchCohortPeers(req, res, fellow, peers);
    }
    else {
      fetchCohortPeers(req, res, fellow, peers);
    }
  })
  .catch(function(err) {
    logger.error(err);
    res.status(500).json(err);
  });
};


var fetchCohortPeers = function(req, res, fellow, peers) {
  models.Cohort
  .findById(fellow.cohort_id, {
    include: [ models.Fellow ]
  })
  .then(function(cohort) {
    if (cohort) {
      _.each(cohort.Fellows, function(peer) {
        if (peer.uid !== fellow.uid) {
          peers.push(peer);
        }
      })
      res.status(200).json(peers);
    }
    else {
      res.status(404).json({
        message: 'Cohort does not exist'
      });
    }
  })
  .catch(function(err) {
    logger.error(err);
    res.status(500).json(err);
  });
};

var fetchPeers = function(req, res, fellow, peers) {
  var where = {
    $or: [
      {
        level: 'D1 Jr Consultant'
      },
      {
        level: 'D2 Consultant'
      },
      {
        level: 'D3 Consultant'
      },
      {
        level: 'D4 Consultant'
      }
    ]
  }

  models.Fellow
  .findAll({
    where: where,
    order: 'first_name ASC'
  })
  .then(function(fellows) {
    if (fellows) {
      _.each(fellows, function(peer) {
        if (peer.uid !== fellow.uid) {
          peers.push(peer);
        };
      })
      res.status(200).json(peers);
    }
    else {
      res.status(404).json({
        message: 'Peers does not exist'
      });
    }
  })
  .catch(function(err) {
    logger.error(err);
    res.status(500).json(err);
  });
};