Actor. Abigail has advantage on Charisma (Deception) and Charisma (Performance) checks when trying to pass herself off as a different person. She can also mimic the speech of another person or the sounds made by other creatures. Abigail must hear the sound or person for at least 1 minute for this to be effective

Alert. Abigail cannot be surprised while she is conscious. She also has a +5 bonus on initiative rolls, and other creatures do not gain advantage on attacks rolls against her because of being hidden from her.

Book of Ancient Secrets. Abigail has the following ritual spells in her book of ancient secrets. Her spellcasting ability is Charisma (spell save DC 17, +9 to hit with spell attacks), and these spells can only be cast as a ritual.
1st level: alarm, comprehend languages, detect magic, find familiar, identify, purify food and drink, unseen servant
2nd level: augury, gentle repose, magic mouth
3rd level: feign death, water breathing, water walk
4th level: divination
5th level: contact other plane, rary’s telepathic bond

Devil’s Sight. Magical darkness doesn’t impede Abigail’s darkvision.

Innate Spellcasting. Abigail’s innate spellcasting ability is Charisma (spell save DC 17). She can innately cast the following spells, requiring no components:
At will: disguise self

Magic Resistance. Abigail has advantage on saving throws against spells and other magical effects, as long as her familiar (an imp) is within 10 ft. of her.

Observant. Any creature’s mouth that Abigail can see that is speaking a language she understands, can be interpreted into what they are saying. This also gives a +5 bonus to passive Wisdom (Perception) and passive Intelligence (Investigation) scores.

Spell Sniper. Any spell Abigail casts that has a ranged attack roll has its ranged doubled and ignore half cover and three-quarters cover.

Spellcasting. Abigail is a 10th-level spellcaster. Her spellcasting ability is Charisma (spell save DC 17, +9 to hit with spell attacks). She regains her expended spell slots when she finishes a short or long rest. She knows the following warlock spells:
Cantrips (at will): chill touch, eldritch blast, guidance, minor illusion, prestidigitation, shocking grasp (uses Intelligence), thaumaturgy, vicious mockery
1st–5th level (2 5th-level slots): armor of agathys, banishment, darkness, dispel magic, dominate person, faerie fire, greater invisibility, hex, hold person, hypnotic pattern

Multiattack. Abigail uses Agonizing Spear twice.

Agonizing Spear. Ranged Spell Attack: +9 to hit, range 600 ft., one target. Hit: 11 (1d10 + 5) force damage, and she can choose to move the target 10 feet.

Dagger. Melee or Ranged Weapon Attack: +6 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 4 (1d4 + 2) piercing damage.

Fey Presence (Recharges after a Short or Long Rest). All creatures in a 10-foot cube around Abigail must make a DC 17 Wisdom saving throw. On a failure, the creature is charmed or frightened, her choice, until the end of her next turn.

Misty Escape (Recharges after a Short or Long Rest). In response to taking damage, Abigail turns invisible and teleports up to 60 feet to an unoccupied space she can see. She remains invisible until the start of her next turn or until she attacks, makes a damage roll, or casts a spell.

Beguiling Defenses. In response to a creature trying to charm her, Abigail can turn the charm back on the creature. It must make a DC 17 Wisdom saving throw or be charmed by Abigail for 1 minute or until it takes damage.

The siblings can take 3 legendary actions, choosing from the options below. They can take only one legendary action at a time and only at the end of another creature’s turn. The siblings regain spent legendary actions at the start of their turn, sharing the same turn and legendary action pool.

Daring Escape. The siblings move up to their speed without provoking attacks of opportunity.

Repel Boarders (Costs 2 actions). Both siblings chastise someone for being on their ship, and take aim with eldritch blasts. They aim at the most armored and/or closest threat to one of them, and fire their eldritch blast cantrip at the threat, aiming to knock them off their ship. At Weak or Very Weak APL, each sibling only fires 1 shot rather than their standard amount (2 at Average, 3 at Strong/Very Strong).

Eldritch Rain (Costs 2 Actions). Choose a point within 600 feet of Abigail. Each creature within a 20-foot radius from that point must make a DC 17 Wisdom saving throw as dozens of smaller, fear laced eldritch blasts bombard the area. On a failure, the creature takes 11 (2d10) force damage, and gains the frightened condition, causing them to use their reaction to move to the nearest area of full cover. They remain frightened and behind cover until the end of their next turn. On a successful save, the creature takes half damage and is not frightened.