Hello All,
I've checked KMB website! If we finally choose to have BBQ on Sat night, we can take Route 91M back to Choi Hung MTR station.

The last bus will be on 11:45pm from Po Lam (Tseung Kwan O). Actually, many overnight buses get pass Choi Hung. Think it won't be too hard for you catching a bus back home! You may take a look of below website to check the routes:
http://www.kmb.hk/english.php?page=search/
Nave, maybe you can take bus route 268C???