How does one pursue legal action to recoup funds by those who may have exploited an elderly family member?

My family has reason to suspect that my grandmother's previous power of attorney had made financial decisions contrary to her best interest, thereby breaking their fiduciary duty. In addition to sums of money being transferred from her accounts without reasonable explanation, the power of attorney also "bought" some real estate from my grandmother. However, shortly after the funds had been transferred into her account, they claim she gifted them the proceeds from the sale. Indeed, they have a letter to that effect and that they claim she signed. Yet, my grandmother denies ever agreeing to such an arrangement or signing such a document. Unfortunately, my grandmother has since passed away, but a deposition exists with her stating as much. The lawyer who was handling the case has recently left the firm, and the executor of the estate is looking for new representation. Is there a case here and if so, is there a specific type of lawyer who would be best suited to handle such a case?