Please, check my sentence! - 2
－这是谁？
－这是我的老师。
－他好吗？
－是，他很好。

－他们都是哪国人？
－他们是俄罗斯人。

Who is this?
This is my teacher.
Is he fine?
Yes, he is fine.

Where are they from?
They are from Russia (they are Russian).

Question

Please, check my sentence! - 2
－这是谁？ 
－这是我的老师。 
－他好吗？ 
－是，他很好。

－他们都是哪国人？ 
－他们是俄罗斯人。

Who is this?
This is my teacher.
Is he fine?
Yes, he is fine.

Where are they from?
They are from Russia (they are Russian).

Answer

your translations are all correct.

Answer

There's no problem,没问题

Answer

－这是谁？ 
－这是我的老师。 
－他好吗？ 
－他很好。 do not add 是

－他们是哪国人？ do not add 都, unless you wan to say "Where are they ALL from?"
－他们是俄罗斯人。

Answer

All correct!