講英文好易令人誤會，點做先好？

非常同意樓上julie的回答。

不是在於加個"，"便改變句子(前後文之間的意義)

你中文句子意思的「乘客少，這些少少的乘客沒受重傷」
根本就不會這樣"A, WHO B"來表達的。

文法上的所謂
non-restrictive relative clause
是指"WHO"後的內容並不是"獨指A的行為或情況，反而是把使用B來定義/理解A。

例如：
The man was seriously injured in the accident, who took this bus to go from A to B.

你的原意：
乘客本來就很少，而且他們逃出來時都沒有受重傷。
這句應該改為
There were very few passengers and they escaped without serious injury.

不過回說你的問題關於講話時如何說出"重點"，假如用你堅持用原句式講：

中文a的意思讀時的重音(或提聲)是
There were very few passengers WHO(that) escaped without serious injury.

中文b的意思讀時的重音(或提聲)是
There were very FEW passengers, who(THEY) escaped without serious injury.

另外順提這種接近反反(double-negative)寫作並不可取，例如a句你中文也不是直譯為
只有少部份乘客沒有受了重傷。

其實英文也應該是
Majority of the passengers sustained major injuries.
便無論讀和講都沒有誤解。

無停頓時又唔需要講得好快, 講得快會令人聽唔清楚
無停頓時, 只需要pas-sen-ger三個音都讀成高音
有停頓時, pas讀高音,sen-ger讀低音, (ger可以讀低到高音)
其實唔駛咁介意人地會誤會, 除左讀起上來既連貫性可以indicate你既意思之外, 讀既時候既語調、神情都可以自然地indicate倒你既meaning, 所以唔駛咁擔心, native speaker都唔會特別諗呢樣野) 同埋好多時句子既context都已經indicate倒係邊一個情況

It is about making a sentence with the meaning that you want to mean. It is not about the sentence structure itself.

You would not use non-restrictive relative clause in sentence (b) if you want to mean 遊客本來就很少，而且他們逃出來時都沒有受重傷。

There were very few passengers and (而且) they all escaped without serious injury.

Sentence (a): 很少遊客沒有受重傷的逃出來 (大部分逃出來的乘客都受了重傷。)

Very few passengers escaped without serious injury.

MY POINT is: when you speak, you will naturally choose a right way (sentence structure) to express your meaning.

Restrictive clause like "This is the man who sold the car to me yesterday." is very typical and should be used in either writting or speaking. (no need to 斬腳趾避沙蟲)

Simply putting a comma in the sentence would not make it non-restrictive, as
This is the man, who sold the car to me yesterday. (in fact, no comma is needed)

2015-05-14 00:24:30 補充：
Naturally, non-restricture clause is seldom used in spoken English. People tend to say it in two single sentences or a compound sentence using conjunction.

When you read a, the stress of the word " passengers "
should be from low to high,

but when you read b, the stress of the word " passengers "
should be from high to low


This method is suitable in any cases