To answer your questions.

Yes Haunt stacks from multiple WD's. Both the dot, the damage buff from the poison one, and the 2p proc work across all the WD's in the group using it. The same is true for almost every single WD damage buff. So Cold zdogs, Piranha damage buff and Mass Confusion all stack. The only ones that don't are BBV (neither the attack speed or the damage bonus of Slam dance will stack) and I am not sure about Hex since I haven't tested it (the damage buff only works while the enemy is hexed into a chicken so I am not sure if multiple hexes can apply to a single target).

Pets don't trigger Sash of Knives or any other item proc for that matter. If you are going 2p Jade and using Poison Haunt as your main spam ability you probably want the belt that makes it hit two targets. 2p Jade Haunt is extremely strong at single target but relies on the belt and area damage to be able to make up for it's poor aoe. That said Area Damage does work with the 2p set bonus, so it is very strong with Haunt.

You can't really fit 6p Zuni into a WD team very well. You should probably want to use the Homonculus mojo on any WD team and that means you can't use the Zuni mojo which makes it much harder to hit 6p Zuni. FnR rings are probably going to be the best thing you can wear as well so that means no Zuni ring or Rorg. So your best bet is to focus on 2p Jade and use supporting items like Quetz helm, Swamp Land Waders, etc.

To make my team tougher, I have an idea of using the Homonculus on all 4 of them instead of just 3. Yes you can get away with only 3 of them needing it, but with it on all 4 you can go from casting Sac every .7 seconds down to every .5 seconds. That may make it easier to keep large groups controlled. The other part of the idea is to swap bracers out to Ancient Parthan Defenders and somehow work Spirit Walk back into my builds.

The goal would then be to SW into the pack and start stunning in order to get the APD defense buff.

I don't have the new mojo's on live right now to be able to test the team effectively from a stunlock perspective. I will most likely play Wizards in season 3 because I don't have any geared Wizard teams atm. I have a partially geared WD team already on non seasons and there is nothing locked into season 3 that would really benefit a WD team, so I will start over with something new for S3.