Hey, glad you enjoyed the adventure and thanks for the kind words!
Yeah I agree haha, the final fight ended up being more lethal than I had anticipated, my suggestion would be just to reduce the HP, the amount of tendrils, remove one or two of their abilities or any combination of those. See where your PCs are at by the time they get to the end and recalibrate accordingly so they don't get minced lmao
I had heard one group had thrown dynamite into the room blowing up both Alexei and the painting. Another had backed off and lurred the tendrils into a previous painting and dealt with them there, some unhinged and also out of the box thinking!
Just some thoughts :]