Hm, you have some good options actually... for instance, Gorgorab, Ultimate Galek, Visix, Sethallia plus an off-affinity tank, don't remember what affinity 15 is. It's maybe a little low on TM control, but you don't have too much else, unless you can build an Armiger maybe. The tactic would be to have UGalek put his AOE HP burn on all the spiderlings and have them kill the spider a bit with every turn they take - if Sethallia and Visix can keep the big spider's TM down enough that she doesn't heal back too much. You don't have too much damage in that comp, but that's the whole point, you don't want to kill the spiderlings fast because then they can't hurt the big spider with their HP burn.
Not sure if this can work for you because of gear differences but you can try similar team that I used below. Sethalia and Scyl as your tank. They can heal each other and Sethalia can put block debuffs which can help a lot.
Sinesha and Shieldguard here are just aoe damage dealers.
A fast Armiger (mine have 220+ speed) can help in keeping the boss from getting a turn.