I'm not very familiar with demonology ((( Where can I find this table about it? And how do I use it? I've seen it a couple of times, but I still don't understand it. ((( Is there a dependency on the number of pits? And is it true that Nimmuus summons more demons? Thanks.

Nimmuus summons the same number of demons as any other creature, like a Fafnir.
7 pits can summon a maximum of 10 demons.
General principle:
--the amount of health of the demons is equal to the amount of health of the killed creatures (actual, taking into account artifacts)
--demons cannot be summoned from non-living creatures
--the maximum amount of health of the demons is equal to the amount of health of the pits (nominal, as far as I know, without taking into account artifacts and damage)
--one stack of pits can summon demons only once per battle
In general, read the topic "Tactics for Inferno".