first thing to do is put brogni and coldheart into your team. shield buffs tend to make or break spider teams at higher levels and brogni's one of the better options in that regard, particularly once he's booked. coldheart obviously is there for her a3. i would definitely drop septimus and probably armina as well, although she could replace fu-shan against spirit affinity levels. if that still doesn't solve your issues, you could look into adding another turn meter manipulator. you could either replace lilitu with scyll, giving you her turn meter reduction on her a1 as well as additional cc and her passive, which does wonders for keeping your team alive, or try putting alure in. she's a great champ, particularly now that you can set her to only use her a1, but only if you can survive without golden reaper's atk down (or fu-shan, but i find spider quite difficult to kill without a def down debuff, not to mention he offers the best aura to your team).

Thanks for the advice!

Yeah, at the moment I'm bringing Coldeheart up to Lvl 60.

I never really thought of the shield buffs as being crucial in the spiders den, I will defenetly try.

Another thing someone in my clan told me, is that I should use Visix in my spider-team. He said, that visix is a great champion for dungeon bosses overall. What do you guys think?

Maybe for now: Golden Reaper - Lilitu - Brognir - Fu Shan - Coldheart 

And in the future, I could Replace Lilitu for Scyll. I indeed like the idea of also bringing Visix in, but I don't know which champion to cut for her.

I recommend the following team:

• Duchess Lilitu (Aura, block debuffs, veil, shield, revive and atk buff)
• Ultimate Galek (places hp burn on every enemy with his A3 when under an atk buff)
• Visix (turnmeter)
• Coldheart (turnmeter, enemy max hp attack)
• Scyl (turnmeter, heal, revive)

Make sure, U-Galek has very low damage (low atk, as low as possible crit chance and crit damage), he is not supposed to kill the little Spiderlings. They shall burn her mother to death. He only needs acc to place his hp burn and defensive stats to survive.

The rest of the team is just to keep you alive (Scyl, Duchess) and keep the turnmeter of the big Spider down (Visix, Coldheart, Scyl A1). Maybe you should disable some of the AoE attacks from Scyl and Visix to prevent them to kill the little Spiderlings. 

Keep the atk of Coldheart low for the same reason, her A1 hits random. I would still put her critdam and critrate high, to do some damage with her A3, where the main factor is enemy max hp. Low atk and high crit would be a good balance between low damage A1 (random hits) and high damage A3 (single target).

Thanks @Skadi!

I like that one. I can not use this right now (I need to farm more food) but I will remember it for the higher levels. HP burn really makes sense in this case (why didn't I saw that myself??).