Under the old copyright legal tradition, the “heirs” would have long since lost their claims.
No they wouldn’t have because they sold the movie rights 40 years ago under the old system and that contract is still legal and still enforceable and they’ve been gipped by a slimy studio.
7.5% of receipts is a tidy sum that they haven’t seen a penny of and it’s been 3 years since the last LOTR was made. Somebody belongs in freaking jail, IMO.