Tarantulas are very unpredictable as a rule. Some docile species can be aggressive, some aggressive species docile. The same is true when it comes to co habitation or communal living. NOTHING is cast in stone, BUT, years of experience suggests that some must rather not be kept in close proximity.
I believe that when spiderlings hatch in the wild, they do live in close proximity, for a while at least. The "aggression" and/or canabalistic tendencies and/or territorial behavior manifests as they grow. It might be safe to keep two or two hundred second instar slings in one container, but as they grow, so does the appetite for siblings.
I for one will never say NEVER, it is just not advised...
PS: What the hell happened to the horse???
Most people are like clouds. The sun comes out when they f*ck off...