All praise is due to Allaah. That which is in the Qur'an is that they (Jinn) see mankind from where mankind do not see them, and this is true, which necessitates that they see mankind in a condition that mankind do not see them, and this does not mean that mankind do not see them in (any particular) condition (at all), rather the righteous and other than the righteous can sometimes see them, but they do not always see them. The "shayaateen", they are the rebellious amongst the men and Jinn. And all of the Jinn are the offspring of Iblees, and Allaah knows best.

Refer to Majmoo' al-Fataawaa (15/7). The Jinn are seen by men only when they take a particular form, since men cannot see Jinn in their original form.

In the above book ("Fath ul-Mannaan"), the compiler brings some narrations pertaining to Iblees being the father of the Jinn:

From them, the saying of Ibn Shihaab (az-Zuhree) quoted by Abu ash-Shaykh in al-Adhmah (5/1644), commenting upon al-Kahf (18:50), that, "So Iblees (Satan) is the father of the Jinn, just as Adam is the father of men...", also reported by as-Suyutee in ad-Durr al-Manthoor (4/227).

And from al-Hasan al-Basri, that he said, "Iblees was not from the Angels, not even for the (length of) a blinking of the eye, ever. But he is the origin (source) of the Jinn, just as Adam is the origin of men." Reported by at-Tabari in his tafsir (15/260).

And also a little earlier in the book (pp. 51-52), from the saying of Ibn Taymiyyah:

And the Jinn can appear in the form of men and animals. So they appear in the form of snakes, scorpions and others. And in the form of camels, cows, sheep, horses, mules, donkeys. And in the form of birds, and in the form of the sons of Adam...

See Majmoo' al-Fataawaa (8/458, 10/406 onwards, and 13/78 onwards) and Minhaj us-Sunnah (8/262). And the Jinn can also be seen by animals, such as donkeys and dogs, as occurs in the Sunnah.