Djins

Sir Richard F. Burton has a fair amount to say about them in the footnotes to his translation of the Thousand Nights and a Night including:

Jinni - The Arab singular (whence the Frence "genie"); fem. Jinniyah; the Div and Rakshah of old Guebre-land and the "Rakshasa,' or "Yaksha," of Hinduism. It would be interesting to trace the evident connection, by no means "accidental," of "Jinn" with the "Genius" who came to the Romans through the Asiatic Etruscans, and whose name I cannot derive from "Gignomai" or "genitus." He was unknown to the Greeks, who had the Daimon, a family which separated, like the Jinn and the Genius, into two categories, the good (Agatho-daemons) and the bad (Kako-daemons). We know nothing concerning the Jinn amongst the pre-Moslemitic or pagan Arabs: the Moslems made him a supernatural anthropoid being, created of subtle fire (Koran chapts, xv. 27; lv. 14), not of earth like man, propagating his kind, ruled by mighty kings, the last being Jan bin Jan, missionarised by Prophets and subject to death and Judgement. From the same root are "Junun" = madness (i.e., possession or obsession by the Jinn) and "Majnun" = a madman. According to R. Jeremiah bin Eliazar in Psalm xli. 5, Adam was excommunicated for one hundred and thirty years during which he begat children in his own image (Gen. v. 3) and these were Mazikeen or Shedeem - Jinns.

Elsewhere in his translation, Burton notes that Jann is usually taken as the plural form of Jinni.

Classes of Jinni include the Ifrit ("pronounced Aye-frit", fem. Ifritah) and the Marid (fem. Maridah) who are usually, but not always, hostile to mankind.

You can look for more on the Jinn in tales of the Thousand Nights and a Night and in the Koran.

Ghuls

Ghouls have their origin in the Arabic/Persian/Indian tales of Alf Laylah wa Laylah - the Thousand Nights and a Night and in their root stories. As such, Sir Richard F. Burton, ninteeth century translator of the Nights, has a fair amount to say about them in the foot notes of his translation. The male Ghul, he paints as a creature who eats human flesh:

Arab. "Ghul," here an ogre, a cannibal. I cannot but regard the "Ghul of the waste" as an embodiment of the natural fear and horror which a man feels when he fases a really dangerous desert. As regards cannibalism, Al-Islam's religion of common sense freely allows it when necessary to save life, and unlike our mawkish modern sensibility never blames those who

Alimentis talibus usi
Produxere animos.

vi. 36

My Latin is both rusty and incomplete, so I can't translate that, but the Ghuls in the _Nights_ are rather fearsome, and do not seem to prey on humanity mearly through necessity. Their appetite is nearly insatiable:

Allah ease thee, O King of the age even as thou hast eased me of these Ghuls, whose bellies none may fill save Allah! ix. p. 152

Even their names are fearsome, such as this one - The-Ghul-who-eateth-man-we-pray-to-Allah-for-safety.

Burton had some additional comments on the female Ghuls and the origin of the word "ghul".

The Ghulah (Fem. of Ghul) is the Heb. Lilith or Lilis: the classical Lamia; the Hindu Yogni and Dakini; the Chaldean Utug and Gigim (desert-demons) as opposed to the Mas (Hill-demon) and Telal (who steal into towns); the Ogress of out tales and the Bala yaga (Granny-witch) of Russian folk-lore. Etymologicaly "Ghul" is a calamity, a panic fear; and the monster is evidently the embodied horror of the grave and the graveyard. i. p55