I'm going to give this a shot so you can understand better.
flukedivana wrote:Hello all, I'm new here.
Welcome. Always nice to have fresh blood here.

- From chart. I saw there are more kinship terms from father side than mother. It's about a society that focuses on men or not ?
Indeed, it seems so.
- I heard in Vietnam they often used kinship terms as pronoun and main from father side, why ?
Any noun can be a pronoun in Vietnamese. It's complex, but there are some shortcuts to avoid causing any offence or discomfort. For example, using first names for those of your generation is common, even among friends.
- Is it true that Vietnamese society focus on the descent of man is essentially a cousin ? I saw they have some word like Ông nội, Bà nôi which nôi mean inside and Ông ngoai,Bà ngoai which ngoai mean outside.
Oh, that's the difference between the mother's side the family (maternal; ngoại) and the father's side (paternal; nội). I guess "inside" and "outside" to show that they focus on the importance of the paternal line.
- Is Kinship term in Vietnamese show position and seniority ?
It does. Old vs young, blood vs in-law are factored in to a certain degree. On a further note, it's important to take note that the pronouns vary somewhat according to the speaker's dialect. Even more, the table doesn't show how to call your aunts and uncles who married into the family (non-blood relatives) and it also doesn't show you how to call your cousins. It's a bit different. Would you like me to demonstrate them?
- Is a conversation in everyday life not necessary to say trai or gái ? example bác trai and bác gái say only bác.
Yes, as long as the context is clear because trai and gái means male and female. Might be important since aunts and uncles and children can share the same pronoun such as bác, con, and cháu. Same thing with nội and ngoại, especially if you're talking directly to the addressee. No need to directly call your maternal grandmother bà ngoại. Just bà will do.
ps.if possible who have reply please send mail to my inbox for an information of native spearker because i need to do a reference. Thanks in advance

Sure, abcdeg and Tenebrarum come here once every while, but if you can't really wait, Unilang has a page on Facebook (same name: "Unilang"). You don't have to join, but you can find posts made by Dzwee. He's Tenebrarum and he's on FB daily. Feel free to talk to him and he'll be happy to help you!

Plus, it's better to do so since I could be wrong. haha