I think that everyone has covered the subject well. They are excited, and want to keep their baby to themselves for now. It’s only natural. Once the novelty of the pregnancy wears off they will probably do more sharing with you, show you the scans etc.
With my previous GC I have just told them to let me know if they want anything, and stood back. I never offered advice, unless asked, and then just said that we used to do it that way, but times have changed. They could then decide whether to listen, or not.
My next GS is due mid-May, and I should be sitting in the plane, right now, on the way to Perth, Australia, where my DS and DIL live. I always planned to take a back seat. This is their first baby, and first GC for the in-laws, who are very excited, of course. Now I will have to be content with even more of a back seat, internet chat and photos. They are keeping the name secret, too. They said that they may just change their minds, and they don’t want any comments about their choice, and I agree. I wasn’t too keen on any of the names chosen for my other GC, but just smiled and said, “That’s a good choice.” though I’m glad that they didn’t choose Pebbles”, which the GC of a friend was named. She DID make her feelings known, but got used to it eventually, and loves ‘Pebbs’ dearly.
Just go with the flow, and I’m sure that you will get plenty of involvement with the little one, if you show them that you’re not going to be a pushy Grandma.