Is this a case of putting the cart before the horse?
It may seem odd, given that this is GRANSnet, but the focus should surely be on the couple and whether or not they want or are able to have children. Being a grandparent is a privilege and I would lie down in front of a bus for my DGC but, and this is a big but, we have no rights over what our children decide. If I am being honest, I think many family tensions arise from the perceived role of the grandparent((usually, but not exclusively grandma)
I hope OP is not obsessing about whether or not she will ever be a granny, for that is a worrying prospect. We have seen on other threads, members moaning because they are not allowed to babysit their grandchild, members who moan about a DIL (usually) whose only virtue was giving birth to to their grandchild, members who believe their DIL/SILs are jealous of the love their the DGC have for the GPs. Not a happy balance. Be happy if your childen are happy and respect their decision.
Just as some women find their role as mother entirely absorbing and their principal raison d'être, I suspect this can get passed on to being a grandma. A woman is surely more than a wife/mother/grandmother .