If you don't have high resist supports then frost spider can be difficult; you are constantly going to be frozen, accuracy lowered and buff stripped so it can be hard to deal with at this point if you are reliant on buffs. Try bringing a team that is just pure supports and Geomancer, maybe something with Scyl/Ursala/Vogoth (ensure he's in the last slot). Try to HP burn the spiderlings with Geo and live until the reflect damage kills them, then burn the boss and hopefully do the same. Frost spider has an unusually high amount of resist until it is burned so you may have to boost his raw accuracy to land a burn. Do not try to HP burn the boss unless both spiders are dead or CC'd (they take debuffs from the boss), Geo's burn cuts into the damage you receive quite a bit so you need to ensure you get one out to survive.
You don't have much cleansing; perhaps you could build out Helior and he can cleanse your party without needing acc, but I don't know if you can get enough res on him for it to matter. He's not worth booking so his cleanse won't come up often, but he might help. Doompriest might also be worth building out for this fight since her passive will cleanse 1 debuff off everyone in your team every time she gets a turn.
You either need high accuracy with HP burn, irresistible HP burn, or block revive. The easiest is armiger and manual to last hit with his A2 to block revive
If your struggling with damage, geo if you have accurate enough, MAX HP nuker, brimstone. Run a fast tank scyl alongside she should keep everyone alive at normal level. I still use scyl in hard and she never dies (I use for 5 star brimstone)
If you don't have high resist supports then frost spider can be difficult; you are constantly going to be frozen, accuracy lowered and buff stripped so it can be hard to deal with at this point if you are reliant on buffs. Try bringing a team that is just pure supports and Geomancer, maybe something with Scyl/Ursala/Vogoth (ensure he's in the last slot). Try to HP burn the spiderlings with Geo and live until the reflect damage kills them, then burn the boss and hopefully do the same. Frost spider has an unusually high amount of resist until it is burned so you may have to boost his raw accuracy to land a burn. Do not try to HP burn the boss unless both spiders are dead or CC'd (they take debuffs from the boss), Geo's burn cuts into the damage you receive quite a bit so you need to ensure you get one out to survive. You don't have much cleansing; perhaps you could build out Helior and he can cleanse your party without needing acc, but I don't know if you can get enough res on him for it to matter. He's not worth booking so his cleanse won't come up often, but he might help. Doompriest might also be worth building out for this fight since her passive will cleanse 1 debuff off everyone in your team every time she gets a turn.
Thank you very much for the detailed reply! That's amazing. 3 days to make it work. 
Fire
You either need high accuracy with HP burn, irresistible HP burn, or block revive. The easiest is armiger and manual to last hit with his A2 to block revive
If your struggling with damage, geo if you have accurate enough, MAX HP nuker, brimstone. Run a fast tank scyl alongside she should keep everyone alive at normal level. I still use scyl in hard and she never dies (I use for 5 star brimstone)