Some sites said 来的 can be used for an emphasis but here it s separate. Can it have the same meaning or something other here?
你们是坐飞机来北京的吗？Some sites said 来的 can be used for an emphasis but here it s separate. Can it have the same meaning or something other here?
Yes, in 来的, the word 的 is used for emphasis. For example, 你们是坐飞机来的吗？You can insert a noun as the destination of the verb 来, 你们是坐飞机来北京的吗？
Meanwhile, 的 also indicates that the action is in a past time.
你们是坐飞机来的吗？= Did you come by air?
你们是坐飞机来吗？= Will you come by air?
If 的 is used at the end of a sentence, it could be for a fixed structure, such as
(1) 是...的，我是坐飞机来的。= I came by air.
(2) 会...的，我会按时到的。= I will be there on time.
"的" here means the action of "来" has been completed.
Thinking about the following scenairo:
Alice lives in Beijing, and her friend Bob is planning to visit her. They are having a telephone conversation:
Alice: 你怎么来北京？How do you go to Beijing？
Bob: 我打算坐高铁过来。I plan to come by high-speed train.
When Bob arrives, Alice and her brother Charlie invite him to dinner:
Charlie: 你怎么来北京的？How did you get to Beijing？
Bob: 我坐高铁过来的。I came here by high-speed train.
"的 - 用在陈述句的末尾，表示肯定的语气。". When used at the end of a sentence, it confirms/ascertains the statement before it. Place "嗎" after it makes the sentence a request for confirmation.
你們是坐飛機來北京的 - You were coming to Beijing by airplane. (a definite statement)
你們是坐飛機來北京的嗎 - Were you coming to Beijing by airplane? (a request for confirmation)