Afflicted Graverobber, Ancient Soldier Varg, and Cerah the Old Explorer

The Afflicted Graverobber, Ancient Soldier Varg, and Cerah the Old Explorer are a trio of bosses in.

Summoning
Rapacious Andrei and Ruined Aflis are available for summoning as soon as the player enters the Cave of the Dead.

Strategies
It is best to take care of Cerah the Old Explorer first, as she will shoot the player constantly with a Dragonslayer Greatbow. She is very agile and will switch to an Estoc if the player gets close. She wears Lucatiel's Mask, Black Leather Armor, Leather Gloves and the Leather Boots.

Ancient Soldier Varg is by far the hardest to topple of the three enemies. He wears full Havel's Set and wields the Dragon Tooth with Havel's Greatshield. Should he be the last one remaining, he will use an Estus Flask.

The third part of the trio is the Afflicted Graverobber. She wears the full Alva Set and dual wields Berserker Blades. She causes heavy bleed build-up and is very dangerous if she catches the player in any sort of stunlock.

All three are capable of backstabbing the player, inflicting often fatal damage in the process. If you must heal or are attempting to flee, watch your back carefully and be sure it isn't too exposed! If you feel like you're getting overwhelmed, jump into the water. They move slower in it while you can sprint through the water, allowing you to reach dry ground quickly and drink an Estus or plan what to do next.

The strategies the Afflicted Graverobber, Varg, and Cerah use make it appear as if they are working together as a team, combating each other's weaknesses:
 *  Ancient Soldier Varg:  The trio's main tank and the hardest to take down, Varg is the slowest of the three, often supported by the Afflicted Graverobber in melee situations. However, his attacks hit quite hard, often staggering players or downright smashing them into the ground. He does use his greatshield often to block, making him prone to guard breaking, just be cautious of your surroundings before you go in for the riposte. He will also heal with an Estus Flask once his health is below 70%, however his health slowly regenerates, allowing you to strike back and negate it.
 *  Afflicted Graverobber:  Easily the most dangerous of the trio in melee situations, the Graverobber should be taken on carefully. She often follows alongside Varg to support him, as she is more agile and can attack much faster than he can, especially considering the fact that she alternates between two-handing one of her blades or power-stancing both of them. She can inflict considerable bleed build-up in a matter of seconds, which will ultimately slow you to a crawl, reduce your stamina, and take off a portion of your life. However, her attacks do have some starting lag, making her prone to parrying. Time it right, and punish her! She is fast and agile, as well as having the most health of the three, but she can be easily toppled if done right!
 *  Cerah the Old Explorer:  Wielding the Dragonslayer Greatbow and being light on his feet, Cerah is the most dangerous at long ranges, supporting his two melee allies from a distance. He will consistently bombard you with greatarrows, knocking you off your feet and inflicting considerable damage, as well as leaving you open for being attacked by Varg and the Graverobber. While he is the most fragile of the group, he is also the most agile, often rolling away or dodging many of your attacks or backstabs. His Estoc doesn't do terribly much damage upfront, but it will inflict severe damage should he manage to backstab you. The best way to take him out is to bait him into using his bow, roll to dodge the arrow as he fires, and then stagger him with a hard-hitting weapon or with the Stone Ring. He lacks poise due to his choice of armor, allowing him to be stunlocked easily. Just be wary, if he is being attacked, the other two will sprint towards him to try and stop you. The Graverobber will usually attempt to backstab you if she reaches you in time, while Varg will attempt to smash you into the ground with his Dragon Tooth.

Trivia

 * Ancient Soldier Varg and the Afflicted Graverobber wear the armor sets of people who are supposedly dead, being Havel the Rock and Alva the Wayfarer, respectively.
 * As a phantom, it is possible to get a Puzzling Stone Sword, Lightning Clutch Ring, Promised Walk of Peace, Dried Root, or a Sanctum Mace.