I guess I was wrong in my assumption. After some researching, it appears you may be correct in that "disclaiming" simply passes your share to that person's children as if the disclaimer had predeceased the property owner (LRDave's DF). In the case of there being no will, state laws of intestate order will prevail.
If DF has a will, and the grandchildren are named as contingent beneficiary(s) or "per stirpes" or ""per capita" are written into the will, Then it appears that the GC would have to disclaim also.
Absent of the above words written in any Will, I think the only named beneficiary(s) can simply disclaim the land and that would be the end.
LRDave never mentioned the existence of a will or what the exact words are in it regarding beneficiary(s). Since his DF is still on this side of the grass, there may be time to simplify the issue and either change the will, or better yet, somehow dispose of the property before he passes.