1 It's not English origin word- it's the Hawaiian name.
2 Why is it suspicious? Many languages have words starting with ng-. I've come across it in two languages I have studied. I find it hard to say without a vowel before it, but I can't for the life of me see what's suspicious about it.
3 The /p/ is pronounced in Khmer, but languages are free to pronounce things their way- it's a difficult sound, so most people don't bother and there are words in English with a silent p at the start. We pronounce the final letter in Paris, but the French don't. Names can change- the Khmer language changes names of places too. I have lived in Phnom Penh and most of the foreigners living there pronounced the /p/, but very few in the UK do that.