You'll need to do major gear changes on your champions... most importantly Coldheart, she's supposed to do two main things: firstly, deplete turn meter with Heartseeker and secondly, deal massive damage in the process (although on stage 9, that damage won't be so big - it scales off enemy max HP, which means you only really get the big numbers in the final stages).
But that means she needs enough accuracy, enough crit rate and as much crit damage as possible. Neither of your two CHs has anywhere near enough accuracy, which should be above 100 now and above 200 by the time you reach stage 20, nor crit rate, which should be 70 percent (Heartseeker adds 30 percent, so with 70 percent you are sure that Heartseeker will always be a critical hit). You gave one of them a stun set - put that on Bellower instead! All of his attacks are AOE, so he can be stunning spiderlings on every single turn he takes. Most of CHs hits will not be AOEs and it's not like you can stun the big spider when hitting her with Heartseeker.
Also, all of your champions are too slow, you need to prioritize speed stats, especially by giving all important champions boots with speed as main stat (if possible).
Edit: Also, you need to ascend your champions - at 3 star ascension, you unlock an extra ability or improvement of existing ability, then at 5 and 6 star, you gain the slot for amulets and banners respectively. All of those can make a big difference.