Yes it is. Here are some words that have a silent G (the letter G isn't pronounced) align assign benign campaign champagne cologne consign design feign foreign gnarl gnash gnat gnaw gnome gnu reign resign sign

The ng sound is a single sound. You're basically humming with the back of your tongue, ie. putting "n" where "g" is. (And no, replacing "ng" with "n" is not acceptable - we can hear the mispronunciation.) You never put a "g" sound at the end of a word that ends in "ng". It sounds as wrong as putting a "d" on the end of words that end in "n".

For hanging and hang out, it depends on sentence stress. As you may know, most words in English have both strong and weak forms, so there are two different pronunciations. If a word has stress in the sentence, we pronounce the strong form. If it doesn't have stress, we pronounce the weak form. Hanging would be pronounced as /'hæŋi:ŋ/ if it has stress in the sentence. Example: a: Is the clock sitting on the desk? b: No, it's /'hæŋi:ŋ/ on the wall. However, if hanging only has normal stress, it would be pronounced as /'hæŋɪŋ/. If hanging is unstressed, it would be pronounced like /'hæŋɪn/ Hang out is usually pronounced as its weak form - /hæŋaʊt/ <- note how the two words have blended together. However, it would be pronounced as /hæŋ aʊt/ if the speaker were correcting someone using the phrase 'hang out.' Long, song, and lung are content words and will almost always be pronounced with stress in sentences.

The "vowel + ng" sounds like the Portuguese "nh" or the spanish "ñ" for me. But it's a different sound from the english "n". I mean, I can perceive the diference between these sounds in words like "sing"and "sin", for instance. From a Brazilian perspective I'd say that there's no "g" sound (I mean a pure sound like in hug), but its sound is different from the english "n" sound. The "ing" sounds like the Brazilian "im" sound in the Portuguese word "rim".

Here is a video about the question you're asking. Brazilian Portuguese is a syllable stressed language. English is a time stressed language. https://www.youtube.com/watch?v=sUMM5eCvi8w