The best way to learn proper English is to read news report, and watch news on TV. Watching TV shows is a great way to learn casual English, slang words, understand culture reference and humor. If you have already watched these shows then you may recall the words used in the following dialogs.

The boy is your NEPHEW.
Game of Thrones Season 3, Episode 8

Nothing personal.
I'd prefer my niece or NEPHEW...
The Big Bang Theory Season 1, Episode 15

for his crippled NEPHEW 120 years ago.
Game of Thrones Season 8, Episode 4

He's my NEPHEW. I love him.
And he's a damned fool.
Game of Thrones Season 3, Episode 9

but your NEPHEW got mixed up
with some pretty nasty customers.
Breaking Bad Season 2, Episode 8