I don't know of any Arabic word that sounds like Shanum. I have looked in both Arabic and Farsi dictionaries and there doesn't seem to be a word like that. It might be an Urdu word.
Shahin is another spelling of Shaheen, for its details see this answer: Shahin, Shadhin, Rakeem and Sarim. Are these quranic names and what is their meanings?
For the details of Rahila please see this page: Rahila