I just threw gas grenades, and used just the smoke grenades to incapacitate them all. No other weapon is required. The aliens in the smoke squeal for a turn or two, and then fall over & die.
Not sure what you mean by this part.
Is it smoke grenades or the gas grenades that were killing the enemy?
Incidently I found the posts Gorlom linked to about half an hour after my post, made sense to look in the announcements threads. Why I didn't look there to begin with makes less sense.