Pregnancy announcement for the grandparents

Hi guys. So we’re trying to figure out how we should tell the parents we’re pregnant. First off we don’t know whether to tell them together or separately. If we tell them together, we think they may know something is up since they are never together unless it’s a rare special occasion and there are no birthdays, anniversaries, holidays etc. coming up. And then the question is how should we tell them? I’d rather do it in a subtle way but not sure what exactly. Any ideas are welcome. TIA