Since it is such a big group.. Airport might not be a suitable place already and there doesn't seems to be suitable location in the East. (Reserved for smaller East shooter outings?)
Other places like East Coast Park and Changi coastal boardwalk can be quite dark at night.
For east coast, nothing much to shoot. For the boardwalk, the walking path is quite narrow and for big group there is likely not much interaction as the group probably have to walk in single file along the pathway.
So 1 suggestion is to change to central location like the marina barrage? great for night shooting..