Should i try harder.

Personally, I wouldn't over read into the "left on read" situation. As a person, I'm not always great at responding right away, and if I forget, then I really forget. lol They may have seen it and thought to provide it in a bit (maybe they were busy at the moment), and then forgot. I think a simple follow up isn't too much. As others have said, if they're important to you, then of course reach out again. But even if it's just obligatory, maybe a gentle follow up would be nice.

Though, I do think it's interesting that your parents don't have their information. If not addresses, then you could even task them with acquiring their mailing addresses. I think it's reasonable for the related parent to acquire some addresses for their side of the family. But best of luck! Either way, I wouldn't sweat it too much.

Ask yourself if you really want them there in the first place. If it matters to you that they're at your wedding, then a follow up is totally fine. If the answer is no, then leave it. I've realized nothing makes you reconsider relationships with distant relatives more than a wedding lol.

I would not keep reaching out to someone who is not responding after reading your message. That would be a waste of time and money that you can save.