Dwarven/Dwarfish Grammar is pretty much complicated and non-continuous.
Singular Form[]
dwarf
eg: Emperor Kruzak: Well, I am the emperor of the dwarfs and the oldest living dwarf, jawoll! (keyword: Emperor)
Plural Form[]
dwarves (pretty rare at NPCs)
eg.: Kawill: He is a jolly fellow and one of the oldest dwarves alive. (keyword: Jimbin)
dwarfs (common at NPCs)
eg.: Emperor Kruzak: Well, we dwarfs produced some of the greatest heroes of all times.
Note: According to Wikipedia, plural form for dwarf was traditionally dwarfs, but Tolkien used the plural dwarves, which has gone into general usage.
Adjective[]
dwarven
eg.: Kawill: I am the great geomancer of dwarvenkind. (keyword: job)
dwarfen
eg.: Edowir: The ancient dwarfen kings forged it using magic metal, which they took from cyclopses who found it in the heart of a fallenstar. (keyword: Excalibug)
eg.: Isimov: The last haven for dwarfenkind. Our last hope for our survival. (keyword: Kazordoon)
dwarfish
eg.: Jimbin: I supply the army with dwarfish beer to keep morals high. (keyword: army)