I believe VIP benefits only transfer to immediate family. I do not think that nieces and nephews qualify as immediate family - I would love to hear if others have found out differently.
Not from Wyndham documentation, but in general, I found this: The meaning of IMMEDIATE FAMILY is a person's parents, brothers and sisters, husband or wife, and children.
All that said -- maybe you can find a path? Transfer to your sibling (parents of the niece/nephew) and they then transfer to the niece/nephew. Sounds messy but maybe doable?