LMAO. Congrats.
You could do what my sister did: invite them over for dinner and at the end have a cake with baby bootsies on it.
My parents are bugging the fuck out of me to pop out a grand kid.
Get deployed to Iraq and let the woman deal with it. That's what I did
"mom dad, great news, IM GAY"
"WHATTT!"
"Naw just kidding, YOUR GONNA BE GRANDPARENTS"