My group finished Death House last week. They took a couple hits from the shadows and a few more from the ghasts, so stopped and took a long rest before going down the stairs to the bottom level. They never went near the mimic door, correctly fearing it was a trap as it was the only door in the basement.
With all of their resources recharged, the max hp gibbering mouther I used as a replacement for the shambling mound was no problem for them. It wasn't able to land a single bite in the 3 1/2 rounds it survived, and the few people that failed saves and swung at each other didn't connect either.
Overall, my players really liked the adventure. Recapping the changes I made:
- Kids weren't starved to death, but alive in a stasis-like sleep, waking when two small dolls on the miniature beds in the dollhouse were touched.
- Replaced Thorn with a twin sister for Rose (also Thorn). This Thorn doesn't talk and is semi-catatonic, but I'm strongly hinting to the party that the two twins can communicate with each other telepathically. (and have been for the 200+ years of their slumber!)
- Replaced the Grick with skeletal rat swarms.
- Last minute change after several players kept asking "where's the baby" - the gibbering mouther had a baby-shaped mass in its center and the cultists called it "Retlaw the Eternal".
Now that it's over, the party is looking around for any descendents of relatives of the kids. Ismark is promising to help by looking in village records stored in the Burgomaster's mansion in exchange for the party's help getting Ireena to someplace "safe". Madam Eva has hinted that the children have a role to play in Barovia's fate. And the Fortunes of Ravenloft determined Ismark will be the party's ally against Strahd, which was perfect since I planned on using the Ismark's marriage hook from The Beast of Graenseskov (DM's Guild adventure) to get them involved in that before they get embroiled in the many sub-plots around Vallaki, the Winery, and the Bone Grinder. Of course, that's all subject to change if they don't take the offered bait.
Both the Sunsword and the Holy Symbol are in the castle, 2 rooms apart(!), and they could have the Tome of Strahd as soon as tomorrow evening's session if they play their cards right (it's in Van Richten's wagon in Vallaki). I've used both Eva and Ismark to hint that a frontal assault on Strahd at this point would be suicide, but with those draws, there's not much incentive to traipse around the countryside.
Luckily, with Ismark as their ally, I can use his pending nuptials and need for an heir to delay his availability until the stars are aligned.