1. You have to many partly developed champs and to less lvl 60. What are you doing with 5 ascended Armigers?
2. Spider 13 is void affinity, so you have no "off affinity tank" to direct the spiderlings to one of your champs. Instead they will attack the lowest hp.
3. The big Spider can only heal when it get's a turn. Champs with turnmeter control are recommended. Scyl (small chance on the A1, and lvl 60, and heal and revive), and Armiger should be in your team.

Yes this is honestly a big problem with me having not enough champs at 60, not being booked, or not having masteries. The Armigers I'm still building, I don't really use them. Sorry if I wasn't clear but I've beaten up to stage 16, it's just really inconsistant and seems like pure luck when I do. It's these stages like 12, 14, and 15 I've tried negative affinity tank on. Who else should I bring besides those two? Scyl was in almost all of my attempts, but even with Armiger I wasn't able to keep his turn meter down before he heals to full.

I think Skadi meant that you need to focus on one champion at a time and to not bring up so many like your armigers. 

 I'd go with Infernal Baroness, Vrask, Apothecary, Scyl and Roric as speed lead. I use a similar team. You'll most likely need full masteries on everybody to get enough damage so the fight doesn't take forever. Relentless gear + revenge accessories + counter-attack masteries are awesome on Vrask. It's amazing what that orc can do! Make sure your tank has the lowest HP and as much resist and defence as you can stack on her.

That would leave nobody to deal damage on the main spider other than through Warmaster procs. From my understanding you need either a enemy max hp abilty or hp burn. I also can't really make any of them tank except maybe Scyl cause the rest are either in my clan boss or arena team.

mordecai + achak

google that, probably will solve your spider problems through 25