Chinese: How to properly say "Hello, is anyone there?"?

Oh, "ni hao” is a polite greeting term, similiar to "good morning", but in a polite way.
As to your question, I think you're right.
The correct translation of hello, I think it is ”哈囉 "hā luō” , or ‘‘嗨 hēi”, and we actually pronounce the Chinese words with the same English pronunciation and even the tone; because basically these two words comes from English, and I think we borrowed it from English long time ago.
Oh, “hello” could be used in having seen someone or haven’t seen someone, right? And “Hi” is commonly used in informal writing like email or having seen someone, but could not be used in haven’t seen someone, right?
As your other questions, what I feel like is as the following. – Oh, I’m an English learner
I’m old though not very old, when I meet people in hiking trails, I always say “Hi” to show we have same interest.
When I meet my old colleagues, not very familiar with, especially bosses, or senior people than I, I would usually say ”ni hao” to show respect.
Normally, when people hike/amble early morning in parks or suburb mountains, they would usually say “good morning” to show it’s indeed a “good” “early morning”.
For young people, I don’t think they like to say “ni hao”, one of the reasons might be: to show they at least know the English word “Hi”
, another reason might be to show they are young and they are willing to make friends.
When I(we) accidentally meet familiar colleagues, I usually would say “老大 – literally means Big Brother to show kindness and attentiveness.
Surname + 哥(兄)/姊 is very commonly used when we meet people with the relatively same ( include some more or less ) ages.
兄弟 literally means brother, but in spoken language, 兄弟我 means I’m Big Brother, you should listen to me.
So, when meeting people you don’t familiar with, don’t say “兄弟我” and you’ll hear it from Chinese gangster movies very often.
But 小兄弟 is a kind and warm term to refer to your younger-generation (you must older than he or her at least 20 ~ 30 years old) to show you are caring about them; But if you are not actually older than he or her 20 ~ 30 years old, you’re kind of showing that you are Big Brother.

Oh, practice English writing too much, I still miss your title question.
Hello, is anyone there(home)?
The Chinese translation is as follows.
(Hello) 有人在(家)嗎? -- This is the most normal and correct way to ask if anyone there (home)