The key things for spider are: AOE control of spiderlings, and TM control of the queen.
With that in mind - three key pieces for your team should be Ninja, Skarg, and Coldheart. Drath is also good for keeping your team alive.
Siegehulk isn't that great. Early on, yeah, you can just wipe the spiderlings out with AOE attacks, but as you get further on, they become stronger and stronger, to the point of eventually not being practical.
Skarg is good because of his AOE true fear - that really helps to control the spiderlings, and also as a bonus, makes the fight much faster. Ninja is good because of his AOE freeze. Coldheart is good because of her 100% TM reduction on her A3.
For the last piece, you probably want someone with more TM control. I would probably go with Mordecai. He has quite a bit of TM control between his A1 and A2.
Drath may or may not actually be necessary. If you find Ninja and Skarg are enough to control the spiderlings, you may be better off just running Armiger for more control on the queen, or even Khatun to just make your team faster.