#5 stays down. (Ignore my roll; it was a crit.)

Two remain, although one has moved out of view and around the corner.

Gerrard:

Dodging the undead’s Rusty Longsword swing, Gerrard again tries to hold his ground.

Acrobatics with bless vs DC 15:  17

Gerrard:

As the creature just barely fails to shove him, Gerrard prepares to strike only to have his allies efficiently down it before he can swing.  

Given the disturbing proclivity of the creatures to rise and continue to fight, Gerrard stoops down with his fiery dagger and slices and the necks of the two bodies laying at his feet.

Fiery Dagger Attack (roll with advantage against helpless foe, critical if hits):  27

Critical Fiery Damage:  29

Fiery Dagger Attack (roll with advantage against helpless foe, critical if hits):  18

Critical Fiery Damage:  25

He then straightens up and prepares to take on the next attacker.

Thwack 

As one creature falls Thwack sees an opening. Before he can move though, his summoned tentacle swings at the last visible creature.

Whether it hits or not he ducks out the door. If the creature still stands he attacks. If the tentacle slaps the creature to the floor he will head across the room until he can see the roaming one. He will then attack it from range.

BA - Tentacle attack 17 for 9

A - move through door and attack 15 for 9

Gerrard reaches down and assures that at least the top two of the three barnacle- and blue-boil-covered corpses at his feet will not get up. They seem satisfyingly inert as he severs their two necks with his fiery blade.

Meanwhile, Thwack's tentacles pull down and tear up the last visible standing invader. It appears to be dead. (A roll: 16)
Thwack leaps over the stack of wet corpses and tears around the corner. He sees nothing down the hallway, but does hear a commotion further down, around the corner of the twisted hall.

But the dead creature he thought he defeated stands back up, once again. The psychic attack he had saved for the creature who retreated, he directs at his former undead foe, instead.
It collapses once more. (A roll: 14)

But it gets up once more. #2, its body barely holding together, sets its sights on Thwack. It begins to stagger toward him.

Peri and Boko may act next.

Boko pulls out her crossbow and aims for the remaining undead’s head.

Attack: 12 Damage: 6

Peri:

Peri leaps through the doorway after Thwack. He sees the undead thing fall twice but it keeps reanimating. Irritated, he stomps twice on its skull. "Stay. Down!"

Attack #1: 25 for 9 magical bludgeoning damage

Attack #2: 15 for 10 magical bludgeoning damage

"Boko, can you move your spotlight so nothin' can get through the main gate? There might be more of these things."

((Save any Bonus Action to see if the thing stops crawling.))

Boko takes down the remaining visible corpse with a sloppy but effective shot from her crossbow. (A roll: 6)

...But this thing just won't die. It stands once again...

Peri takes a crack at it....
Hit... it goes down (...a roll: 21) 

...and again for good measure (...a roll: 6) 

...And still, it stands, its body nearly torn to pieces from all the damage.

Forgetting Thwack for the moment, the thing swings its rusty blade at Peri.

(...but first, Peri may have his BA.)

Peri:

This damned thing just won't stop! he thinks. He aims a flurry of kicks at its neck, hoping to sever the head.

FoB #1: 24 for 10

FoB #2: 23 for 10

Peri's third and fourth hits also seem to kill this undead horror... (Some rolls: 23,  6)

...and his final strike seems to do the job, as the grotesque, blue-boiled body falls into several inert pieces. It's down.

The kitchen and scullery are clear of undead, but pounding and splintering can be heard down the hallway to the west.

Thwack, Qivys, Gerrard may act next!

Gerrard:

Moving forward as he slices at two more corpse necks, Gerrard ends up in the hallway to the east of the Moonbeam.  He looks west to see if he can see the corpse that might be banging on the next door, or indeed any more incoming threats.

(Two more fiery dagger attack/crits on downed corpses that look more or less intact and perhaps capable of rising.  Then move out into the hallway but not into the Moonbeam.)

Perception:  18

Gerrard:

(Please ignore duplicate post from poor internet connection)

Gerrard ensures that the downed corpses are indeed downed. Then, joining Thwack on the north side of the scullery, and looking west past the moonbeam, Gerrard finds that he cannot see the last Drowned Blade, but he can hear something banging and splintering just out of view, around the corner. Getting any closer, however, requires crossing the beam. It sounds like a single creature, not a whole mob, and the sounds seem to be inside the building, not outside.

Thwack and Qivys may act next!

Qivys will move out into the room where Thwack and Gerrard has moved to, shield and axe in tow. He will scan the bodies, making sure none are "coming to life" again but will not touch any of them.

"Don't need no blue beauty marks on me." he mumbles. 

"Where'd he go." Qivys will ask Gerrard. 

Gerrard:

"Sounds like it is down the western hallway---we need Mistress Alcor to move the fiery moonlight so we can safely proceed," says Gerrard as he stands up from slicing a flaming line across the corpse's throat.