is है wrong here or is it omitted for ease of speech?
It is often omitted when the sentence is a negation, but there is nothing wrong with including it. Fun fact: aparently the historical word for no was न, and नहीं was a contraction of न + हैं.
We do not like oranges.
Difference between हम and हमें?
In a previous similar sentence I wrote the nehi after the pasand, and it was accepted. Are both ways OK?
Yes both r ok
संतरा juice अच्छा है