How can the agent of a devil “capture” a soul in D&D?

Devils always want more souls for the Blood War. Mostly, they get those from lawful evil mortals. But as various lore – and this question What groups of souls go to the Nine Hells according to lore? – make clear, pacts with devils and even magical accidents can also cause a soul to go to the hells.

In my game, one of the party (a Warlock) owes a favour to a devil (their patron). I’ve decided that this favour will be to "claim" the souls of two NPCs in the town where they’ve just arrived. The devil in question is Dispater and the town happens to be home to two master blacksmiths, who Dispater would love working in his armouries for all eternity.

Presumably, the most effective way for our Warlock to go about this – if they choose to accept the task – is to try and tempt them with some kind of Faustian bargain so they will make a pact of their own. However, I’m bound to be asked whether there’s any other method. Is there?

Can an Aberrant Mind and Clockwork Soul Sorcerer replace two spells at level up?

All sorcerers are allowed to replace one spell they known when they level up:

Additionally, when you gain a level in this class, you can choose one of the Sorcerer Spells you know and replace it with another spell from the Sorcerer spell list, which also must be of a level for which you have Spell Slots.

Moreover, the Clockwork Magic feature let the Clockwork Soul Sorcerer replace one of their spell known at level up:

Whenever you gain a sorcerer level, you can replace one spell you gained from this feature with another spell of the same level. The new spell must be an abjuration or a transmutation spell from the sorcerer, warlock, or wizard spell list.

Same for the Psionic Spells feature of the Aberrant Mind Sorcerer:

Whenever you gain a sorcerer level, you can replace one spell you gained from this feature with another spell of the same level. The new spell must be a divination or an enchantment spell from the sorcerer, warlock, or wizard spell list.

My question: can the Clockwork Soul Sorcerer and the Aberrant Mind Sorcerer swap two of their spells at level up, as long as one is from their "normal" list and one is from their origin?

Or, do these Sorcerers have to pick to either replace a single one of their Sorcerer spells using the general rule, or replace a single of their origin list using the special Clockwork Magic / Psionic Spells rules?

Celestial Warlock’s Radiant Soul: are there any radiant or fire spells?

So my Celestial Warlock just hit level 6 and gained the Radiant Soul feature:

Starting at 6th level, your link to the Celestial allows you to serve as a conduit for radiant energy. You have resistance to radiant damage, and when you cast a spell that deals radiant or fire damage, you add your Charisma modifier to one radiant or fire damage roll of that spell against one of its targets.

I’m having trouble finding Warlock spells that do Fire or Radiant damage, though. Hellish Rebuke (which doesn’t really mesh well with the Celestial theme) on the Warlock spell list (PHB) and Guidance, Flaming Sphere and Flame Strike from the expanded spell list.

Am I missing something, or is this ability just not terribly useful? Does this ability come online later, with Mystic Arcanum?

How is the Soul Knife Rogue’s Bonus action attack effected by a multiclass with Monk?

So the Soul knife rogue has a feature as follows:

After you attack with the blade, you can make a melee or ranged weapon attack with a second psychic blade as a bonus action on the same turn, provided your other hand is free to create it. The damage die of this bonus attack is 1d4, instead of 1d6.<

As is, the psychic blade is a simple melee weapon and as such qualifies as a monk weapon.

I think its fairly obvious that the original 1d6 of the blade will increase as a monk weapon would normally do, but does the bonus action damage also increase?

Can another player benefit from the Phantom Rogue’s soul trinkets?

At level 9, the Rogue’s Phantom subclass (Tasha’s Cauldron of Everything) gets the ‘Tokens of the Departed’ feature, allowing them to create ‘soul trinkets’

When a life ends in your presence, you’re able to snatch a token from the departing soul, a sliver of its life essence that takes physical form: as a reaction when a creature you can see dies within 30 feet of you, you can open your free hand and cause a Tiny trinket to appear there, a soul trinket.

These trinkets have a couple of uses, one being:

While a soul trinket is on your person, you have advantage on death saving throws and Constitution saving throws, for your vitality is enhanced by the life essence within the object.

Given that you can have more than one soul trinket at a time (up to your proficiency bonus), it’s tempting to pass them around. It’s unclear whether the quoted soul trinket benefit is a property of the trinket or of the rogue, and hence unclear whether another character holding a trinket would gain advantage on death and Constitution saving throws.

Does a Divine Soul Sorcerer have access to the additional cleric spells in Tasha’s Cauldron of Everything?

Additional Cleric Spells

1st-level cleric feature

The spells in the following list expand the cleric spell list in the Player’s Handbook. The list is organized by spell level, not character level.

Divine Magic

When your Spellcasting feature lets you learn or replace a sorcerer cantrip or a sorcerer spell of 1st level or higher, you can choose the new spell from the cleric spell list or the sorcerer spell list. You must otherwise obey all the restrictions for selecting the spell, and it becomes a sorcerer spell for you.

Do the additional spells count as being on the Cleric’s spell list for the purposes of Divine Magic as long as both supplements are agreed to be used?

Stealing a beholder’s soul [closed]

So I kinda half-assed a session yesterday where the party found a unscathed beholder skeleton which was feasted upon by gas spores and made a town sick. I just have this idea that the beholder had its soul stolen by some monster or was put in a phylactery. I’m thinking a night hag but I can’t think of a way to implement it or any of the other options.

Can a multiclass divine soul sorcerer / wizard add cleric spells to the spellbook?

I am in a campaign where I am a level 2 sorcerer and level 1 wizard and I have a paladin, a cleric, and a druid in my party. I was wondering if I am a divine sorcerer and have access to the cleric spell list, can the cleric or the paladin write cleric spells in my spellbook?
Or if I find or buy cleric spell scrolls can I add them to my spellbook?

Why? or Why not?