Ok first of
Ana has a weapon that make it harder to treat wounds
Given that the CCW bans the use of undetectable shrapnel that would prevent treating of wounds i have to assume this would be banned at some point-
(though technically the CCW lacks and enforcement mechanic)
I mean your not even allowed to use hollow point or teargas in war… so yeah forget using offensive biotics.
Secondly both Junkrat and Hammond make use of landmines which violates the Ottawa Treaty (aka the Mine ban treaty)
this is also covered by protocol II of the CCW (Aka the Inhuman weapons convention)… technically they can be allowed but you have to keep track of where they where placed for later removal.
Mei could also be argued to be a clear violator of the geneva convention covering the treatment of captured prisoners of war… since she can clearly capture people yet insist on shooting a spike of ice through their brains…
Regarding torbjörns and symetras turrets… while there are no treaties on this at the moment that cover them, there is clearly some growing concern about autonomous weapons systems and there as been some work on covering this under the CCW
I’d also argue that Pharah uses carpet bombig which may endanger civilians.
and that Moiras orbs clearly are very wild unguided munitions that could also endanger civilian populations. (at this point i am a bit to lazy to look up the relevant treaties and agreements.)