You may want to research "non-qualified disclaimer" since as you mentioned, this would not be considered a "qualified disclaimer" since it falls outside the 9-month window. As I understanding it, the heirs disclaiming wouldn't be taxed because they are disclaiming it, but now the gift tax comes into play. I'm not a tax professional, but I think it does come down to being considered a gift and needing to file gift tax returns b/c the value goes beyond the annual $15k exclusion. But that doesn't mean they need to pay taxes on it - but they do need to file gift tax returns. Again, I'm still researching a similar situation myself but related to retirement accounts, not real estate.
If you've learned more in the meantime, please post.
