I presume that you are actually able to comply with the request.
Certain information on beneficiaries is required as part of the process of applying for probate.
If the death was that of a close relation, I would think that writing to you so soon, and imposing such a peremptory time limit, is insensitive. In your position, I would tell the solicitor so in the hope that he or she might be more considerate in future cases.
[I have just copped on that this is part of an ongoing saga. You might need to have your own legal advisor.]