Conjoined souls

Ethereal Sight. The Conjoined souls can see 60 feet into the Ethereal Plane when it is on the Material Plane, and vice versa.

Incorporeal Movement. The Conjoined souls can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

Begrudging Allegiance. The Conjoined souls must command its masters orders, but if someone impersonated them or commanded them with the chains they could possibly control them for themselves.

Freed at last. If the chains are broken, they are unsevered, and/or the Conjoined souls hp reach 0 they are instantly sent to their respective afterlifes wherever  that may be.

Withering  Maul. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 17 (4d6 + 3) necrotic damage.

Multiattack. The Conjoined souls can use withering maul twice.

Spiritual Bedeviling   (Recharge 2). One humanoid or beast that the Conjoined souls can see within 5 feet of it must succeed on a DC 13 Charisma saving throw or be possessed by the Conjoined souls; the Conjoined souls then disappear, and the target is incapacitated and loses control of its body. The Conjoined souls now controls the body but doesn't deprive the target of awareness. The Conjoined souls can't be targeted by any attack, spell, or other effect, except ones that turn undead, and it retains its alignment, Intelligence, Wisdom, Charisma, and immunity to being charmed and frightened. It otherwise uses the possessed target's statistics, but doesn't gain access to the target's knowledge, class features, or proficiencies.

Whist the Conjoined souls are in the body, it causes the body to convulse dealing an 1 (1d10)

The possession lasts until the body drops to 0 hit points, the Conjoined souls ends it as a bonus action as a response to a direct command, or the Conjoined souls is turned or forced out by an effect like the dispel evil and good spell. When the possession ends via command the Conjoined souls reappears in an unoccupied space within 5 feet of the body, but if it ends via the death of the being it possessed it'll rip out of it in a fatal mater skipping death saving throws. The target is immune to this Conjoined souls' Possession for 24 hours after succeeding on the saving throw or after the possession ends.

Chain Whip. If the chain happens to be free, as in not hooked on to or apon something or in someone's grasp, It can whip this huge powerful chain at a target dealing 1d4 bludgeoning damage