It's strange, I'm playing on normal difficulty, and I only have 2 more demon portals to clear. Nastya has 50 weavers, 80 vampires, and almost a hundred liches. Lyudmila has almost 900 skeletons, 300 ghosts, and ghouls... you're probably lagging at the start + you're suffering big losses.

Read more carefully. Somewhere around the first month, I had a week in the description that said the creature growth in castles was reduced threefold. But in the calculations, there seems to have been a glitch, and everything went into the negative. I even checked specifically: I have -159374 skeletons, -105190 ghouls, -101924 ghosts, -57316 liches, -76476 lamassus, -70000 vampires, and -25512 weavers.
And Necropolis can't really suffer losses. You could even call it a cheating race.