This sounds VERY familiar. We to have been told similar things.
They are too old to do anything different. It scares them to even contemplate leaving the borg. It is ALL they know. It is like the movie the Truman show.
If your family wants to continue to believe this, even if it is not true, so be it. If they choose not to associate with you or your family, it is their great loss. As much as it hurts, it is their choice and we may not understand why but we have to go along with it or it will drive us nuts thinking about it. This is what we have decided to do. When we are with our still in family, it really is just small talk and casual conversation. When WT subjects come up we just sit there and smile and keep quiet. It is just too frustrating going head to head with them. They all know how we feel about WT and we will not continue to argue with them.
WT is their comfort zone. Their warm blanket. It makes them feel safe, warm and cozy. If they left that comfort zone and went and lived in the real world, I just don't think they can handle it. WT tells them how to feel, think and live. Doing anything without WT is scary. It is a VERY sad way to live.