Advice on Announcing?

Ashley
Hello ladies,
So we intend on letting my in-laws know they they're gonna be grandparents this weekend over dinner. My husband's family is very strange to me, because they don't express emotion and affection very much, whereas my family always jokes and hugs and cries together.  We aren't exactly sure how to broach the subject or what wording to use to tell them that isn't going to result in too awkward of a situation. Any advice?
Thanks in advance!
(Also, the Little Seed will only be 5 weeks, 3 days when we go to dinner with them.)