M.L.
When my father died, my mother did not grieve in a healthy way. In all truthfulness I almost had her institutionalized, because of her terrifying and erratic behavior, the way she isolated herself. Even her grief counselor was worried and said she was refusing to find peace.
There is a healthy way to grieve and to preserve memories. Perhaps the mother is not letting you see the grandchildren at this point, because she is trying to create as normal an environment for them, but you are so focused on your sadness that you can't push past that, and it is a scary and unhealthy thing for the little children to see. Which, I'm sure you would agree.
I strongly urge you to seek professional grief counseling. After 7 months of his death, he deserves a burial plot, so that his memory can be shared in that place. His widow and child deserve to go to a place where they can visit him and see his name. I think it is very kind they are waiting on you to help decide, if it was my husband that died and his parents refused to see the reality of the situation, I would go ahead and make those decisions myself.
Yes, it is very hard to lose a child, it is also hard to lose a spouse and a father, so there needs to be some compassion for them as well. Something my mother never gave me.
You will never let go of your Abel. Putting a plot on the burial site and having comfort and joy in life is not letting go of him. It's embracing and honoring his memory. He wouldn't want you to be depressed and incapable of functioning.