......As a result, the news in letters was already out of date when people received it.
1) Is it better to use "were" in this case as we are talking about news in several letters?
2) also should I use "had been" instead of were?
"news" is always used with a singular verb, so you'll need "the news was". "in letters" clarifies which news "was already out of date".
news (no͞oz, nyo͞oz) pl.n. (used with a sing. verb)
Re: question 2, because it's a single event (when people received the news, at that specific moment in time, it was out of date), you want the simple past (was, rather than had been).