"My grandparent told me a lot of stories about the past, and it was such stories that help me to understand more about the difficulty that he used to face"
I just want to use the structure "It was ... that" to emphasize. Is it grammatically right or should I write "they were such stories that?". However, "they were.... that" doesn't seem right to me, it sounds peculiar.
Can you give me some advice since I am not a native speaker? Thanks so much.
The dummy subject "it" introduces an extension of the topic in your sentence. The real import of your statement goes beyond the mere fact that there were stories to explain what those stories meant for your understanding of your grandparent of his life. So your instinct to use "it was" instead of "they were" was a good one. You don't need number agreement with the previous clause.
(Note that you should keep the verb tense the same: "My grandparent told me ... such stories helped me ..."; and there were multiple stories, so I'd pluralize difficulty: "the difficulties he used to face"; also, why "grandparent"? You identify him as male, so why not grandfather?)
