几 in declarative and interrogative sentence
I think all the sentences with 几 above can turn into interrogative sentences. For example:


  后面有几个人笑起来了? 
  
  你家有几口人?
  
  上海有几个火车站?


In the mainland mandarin, we usually put 好 in front of 几 in the declarative sentence to indicate that there are more than one. For example:


  后面有(好)几个人笑起来了。// 好 can be omitted without changing the meaning.
  
  你家有好几口人。// 好 can not be omitted
  
  上海有好几个火车站。// 好 can not be omitted


With 好，you can differentiate if it's a declarative or interrogative sentence.  In some sentences (like the first one above), 好 is omissible. You'd better not omit 好 in the sentence 2 and 3, otherwise they would sound like interrogative sentences.