Legally, IMO, Notorious B.I.G’s estate is in a relatively strong position to have relief granted by the court.
1) Any potential suit by the original authors may, in fact, be time barred. They have long had notice of the use of the sample without filing an action.
2) The next issue is what was infringed? The answer, in this case, would at best be the sound recording. It would be very difficult to argue that two notes, especially when rearranged and transposed would amount to infringement of the underlying work.
3) The third issue, is whether or not the alleged infringing use would, or did, cause economic harm to the original. In this case, it may well be that the original work would benefit from the attention brought to it, by B.I.G’s use.
A strange set of circumstances indeed. For two notes, the producer of the original work wants to claim 50% ownership if B.I.G’s song.
It would be hard to imagine that the court would not see that as a stretch, longer than the late B.I.G’s limo.