There is a similar situation over on another BB’s that I belong to. A member there has fallen under the influence of another schismatic group.
We have seen him go further and further down the slippery slope of the groups influence (he even was a seminarian at one point). Trying to explain things to him in a rational manner only brings out a violent reaction from this person (he has implied the threat of a lawsuit a number of times).
In your situation, as in mine, there is not much you can do since you are not in direct contact with the person. All I can say is to continue to present the facts and pray for a conversion of heart for this person.
PF