Lol. Got them on my 2nd try at the Spire, then found them at the Depths... yeah, no. This is what Alt F4 was made for.

Ok, so I've tried this boss for an hour and the Cannoneer was hitting like a freaking truck...
I've never did this with any boss but I stacked fire resistance like crazy and after that, everything was easy (because I've already learned the movie set from both of them). Next attempt , I've got it.

Fighting Solo (I really like the challenge, I did one boss fight with a companion and I thought it was way too easy).
Set: Night Claw +9 (fire resistance), Nagimukuro +8, Hanemukuro +7 (with fire modification).
Code: Queenslayer.
Passives: One handed sword mastery, avvy Evasion, dex/strength +, Concentration .

I know that people tend to go to the comment sections trying to find a trick to make a boss really simple, but my solution is this (and I know some people won't like this) :
Use fireproof tonics , learn each movesets , concetrate on Blade Bearer and more importantly get good.

I was an hour into this figth when I figured that the Cannoneer was hitting like a fu... truck.
So, the best strategy for me was to stack fire resistance like crazy and then give it another try (I beat it in the next try)
Fighting Solo, so If I was able to it, anyone can do it, and if you have companion, you should be able to have a better time than me.
You just have to focus on the Blade Beared, have fire on your weapon, get behind the pilars, avoid taking damage from her, her moveset is really easy to learn.
There is no really easy way to beat this, you just have to practice , understand the patterns and try to stack resistences to avoid the insane damages.

1

lol so easy. killed both on 2nd attempt as a dark mage
yakumo aggros on blade bearer while you spam guard of honor ice spell to nuke down cannoneer
after, spam ember reversal on blade bearer which absolutely destroys her. super easy fight.
i can see how it would be harder as melee though

honestly, all the guides out there (even here) try to say to attack cannoneer first. this is horse-crap imo. he is the slowest, and easiest to predict out of your peripheral. he also is a meaty boi, so time spent trying to whittle him down is time for blade bearer to do the real hurting. best to go in with fire lily/blazing roar/flame spike/etc set on a high mind/will build, any spell that can hit her despite her speed and with a quick cast animation. she will melt long before you die to cannoneer. also, in my experience at least, she REALLY loves to chase you over any partner you have, so its like the game is tryin to tell ya to deal with her first anyways. oh, and this should go without saying but despite it making you more frail, i would suggest a build with quick dodge, you DONT want to be caught off-guard by fat rolling lol

Fighting Solo (that's how you play souls games).
Set: Night Thorn, Juggernaut Hammer Stun Modification
Code: Queenslayer.
Gifts: Stun Buff, Fire Buff, Cleansing Light, Precision.
Other Gifts are up to you.
Fight over before tonics fade.
Dodge and just land counter attacks on BB. Run around, let her come, dodge, counter, damage gift if you have. Repeat.
CC is a joke alone.

I ended up watching that one boss fight archive YT channel's vid for this fight. After failing with the strategy listed in the guide above, I found the YT vid more successful. I chose Louis's code and brought Io. With fire, attack buff, Yakumo stagger and def skill, as well as awareness of fire circles on the ground-- was able to beat the bosses after forever. Used a +4 fire bayonet cuz I was broke. Used a lightweight +9 blood veil. Good luck!

For those out there that are still struggling with this boss fight, I'd like to share a few tips that helped me through, let's begin: When the battle starts, go after the fatso first, I know this may sound stupid but taking down the Cannoneer is much better than try and fight Blade Bearer while this fat boi is around. You guys know him too well to know what I'm talking about, he'll burn you to ash if you don't give him enough attention and with Blade Bearer's combos of doom, you'll certainly die within five seconds. Bring Whackumo to battle with you, Blade Bearer hates him and will most of the time chase him around the arena and leave you free to deal with her fat friend. Cannonneer is not a big fan of Whackumo either and will try and help his partner to bring him down ASAP with dem AOE attacks. Use this chance to beat the crap out of him, just keep an eye on his AOE attacks when he use them against you and the pimp slap, he will eventually remember that you exist and will try to swat you away, Anyway, don't forget BB, she's fast af and sometimes she'll suddenly appear in fron of you, get the hell out of the way, she'll try to Stinger you as soon as you're within range. When they're close to each other, keep your distance, use this chance to heal, reposition or do whatever you need to, if they don't split, try to lure BB away from Cannonner, hit her twice and back off, repeat until you get her attention, just watch out for the fire and ice storm. Once Blade Bearer distances again, approach Cannoneer and beat him again until you get him killed, it'll take some time but as long as you don't get greedy, you should be fine. For the weapons and mobility, make sure they're at least normal speed, heading on with anything slow is a done deal with death. Louis's Enduring Crimson is pretty good for this battle, Zweihander is a great second option, especially against Cannonner since he's not that fast, as for Blade Bearer, you'll want to use Enduring Crimson, it'll allow to keep up with her insane speed. If you got the DLC equip Venous Claw for some extra speed, it's a pretty good Blood Veil with tons of Drain Attack and Gifts DMG, it makes you kind of a glass cannon tho. If you still need somre more speed, you can try to equip Revenant's Ambition. Hope it helps.