leshy is the easiest of the four and I don't think they will have any trouble defeating him.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103869087/1B0D806F7B5D4CD4ACF6FC8A574AEFB26872DA4D/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

to defeat him you need to unlock the Fleece of a Cursed Crusade which is unlocked in the post game.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103870661/A79701F3BFA70B9E037160EA502DCA4E8C788916/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

I recommend facing him in the purgatory boss rush mode. Once inside the boss rush, look for the Cleansing Fire curse.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103866354/265A0DC94F7A20CE9D7A6BEE0F501F69EA9B513D/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

once you are facing leshy, shoot him as close as possible so that the three projectiles connect. if you did everything right, you will have won without giving him a chance to counterattack.

EXTRA: A relic that helps a lot is Beak of the Fowler as it fully recovers your fervour and allows you to shoot more times.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103972755/FE195E6281B6119B3B6D0A80B4B8ED666648FF16/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

For heket we just need to repeat leshy's strategy but in this case we need to be especially fast to be able to skip the phase where he takes out two mini bosses, I recommend to take the same relic previously mentioned, be patient and don't get desperate for quick damage, the key is to wait and take the windows of opportunity.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103868120/A7078120D38B09B1F5D1D69AF6389512C213F2AE/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

For kallamar the strategy changes I still recommend wearing the same fleece but the curse we will be looking for will be divine guardian.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103864960/9F28741CA574BB94164D77FB101BBEC42773597F/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

This curse will do some damage (although we are not interested in that part), it will give us two seconds of invincibility and it will reflect the enemy projectiles, this means that if we occupy it at the exact moment in which kallamar fires his projectiles these will be reflected to him and will do massive damage killing him instantly, I recommend using the same relic already mentioned.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103868611/F8AB3F5F933CF0EF8C3089E5BED0F4BCD5589EDF/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

this bishop is the one I found the most difficult, do not despair if you do not succeed at the first try.

EXTRA: You can still use the strategy we use with the rest of the bishops, but it is much more difficult and less reliable because there is not much of a window of opportunity to hit all three projectiles.

For shamura we only need to repeat the strategy we used with leshy and heket.

EXTRA: Try not to stand still the spiders that shamura summons will be constantly falling on you.

https://steamuserimages-a.akamaihd.net/ugc/2466357203103869930/E9576D3D00314D39857F9BFB7178E81E6FA697AF/?imw=256&&ima=fit&impolicy=Letterbox&imcolor=%23000000&letterbox=false

This is the first guide I do I hope it helps someone, sorry if my English is bad it is not my first language and at least from my point of view the images I used as a reference only come out as links sorry that I do not understand how it happened.
bye