What do others think

This does seem unusual and odd to me. Perhaps being known as an honourary aunt and uncle as some friends are seems acceptable but grandparents no. Have they been waiting a long time to become grandparents and despaired of it happening. Do the other set of grandparents go along with it. What are your daughter and SiLs views on this......I think it's their place to sort this out really as they are friends of your SiL. Maybe these people have played a significant role in your SiLs life at some point and there is a reason for this which you don,t know about. Think you should tell your daughter and SiL how uncomfortable this makes you feel and take it from there.

I would be very annoyed in this situation, but hope that the arrival of their own GC quells them a bit. My daughter living in the US had an older couple who became very, very friendly with them and spoilt my grandchildren with gifts a bit too much, but they were also very supportive (as when dgd arrived, they kept dgs with them over night) so I let it go. Eventually DD, SIL and kids moved away - but they would even fly out to see them several times a year. Now they have their own grandchild and things have indeed calmed down. But I must say, even with the 'Auntie' thing that many kids call their mother's friends, I think it misleads children and confuses them as to who they are related to and who they are not, as some other posters have said.

It might be harmless but I know I wouldn't be able to turn the other cheek so to speak it would annoy me I think it's wonderful when older people take on surrigate grandkids if those grandkids have NO. grandparents but to argue with you that the new baby will be their fourth grandchild sounds very over powering and blooming weird after all you d expect their first grandchild to be their be all and end all especially if they ve waited a long time and although the nice me says let it go I m afraid I don't think I would which probably makes me a right cow

Maybe your daughter and son in law kindly asked this obviously lovely couple if they wanted to be called and treated as grandparents by the children. Now they are going to be grandparents in their own right I think their response, that to them they considered this as their 4th GC was perfect. You may have been very hurt if they'd responded that yes it was their 1st GC, ignoring your own GC. Get them a card and little gift when baby arrives. Be happy for everybody.

That's a very good point 123kitty

I don't think the poster would have been disappointed at all if they had acknowledged it was their first grandchild after all it's what she expected..... for them to be estactic about their first and only grandchild being born
Of course I agree with the card and congratulations (..... on the birth of your first grandchild ?)

Perhaps they didn't want the daughter to feel that her children will be forgotten now that their own grandchild is on the way.