*.............thanks for asking for me.
This has become a common problem these days; someone devised an estate plan for these people but didn't update it as time went by and the estate tax - unified credit changed several times. In fact, since the gift & estate tax were basically combined, the original "plan" may not have been appropriate anyway, depending upon the value of all of the properties, the nature of the properties and the amounts transferred.
For example, if the owners occupied a personal residence that was included in their real estate LLC and were counting on the Annual Gift Tax Exclusion for their lifetime transfers, it's unlikely that the real estate transfers were effective in terms of the annual exclusion as that exclusion only applies to a present interest as I'm sure you know.
Given that, the original plan was probably flawed as the lifetime gifts of interests in real estate would have used up portions of the unified credit as they made these gifts.
Did the original owners transfer all of their ownership interest in the LLC prior to their death?
Did they actually transfer the shares of the LLC to their relatives?
Did they file Gift Tax Returns on Form 709?
One thing that I've seen done in similar situations is that when the owners don't give up possession of the real property (in the case of their residence for example), there is actually no completed gift because they haven't given up possession of the property.
Basically, and I have no idea if this could apply to your situation, there was actually no completed gift and the LLC holding the real property is actually still owned by the original owners. Again, the facts and circumstances would have to support such a finding.
If there was commercial property involved, what kind of tax returns were filed, who received the rent, etc. Often, these "transfers" are made of the shares but the owners retain the rent report the rental activity on their own tax return, etc. Again, these facts would support that there was actually no completed gift.
There's really no way out of this unfortunate situation.