He has a track record for this sort of nonsense, and if we were in the Lounge I'd say what I think of him, but we're not
He has copyright in the words, and he may have legal ownership of the physical letters and so on, but he has no control over what people say of Joyce, since Joyce is dead. Morally, as opposed to legally, I think there's case for saying that you shouldn't say/write untrue and offensive things about a dead person if it will upset living friends and relations, but I don't think it should be a sueable (I'm sure there's a proper word for that) offence.
Emma