I have a different answer.
The tax preparer
needs to take personal
and professional responsibility here...
If you have sent your check in to IRS, this should be the end of your obligation....
DO not deposit the check. Send it back to IRS with a letter telling them that the preparer made the mistake.... (or have the preparer do so).
If anyone writes a check to the other person it should be the tax preparer or IRS.
You should not be forced to deal with this other client at all. This will only complicate things, and there will be no clear paper trail, as it relates to your obligation to IRS and his obligation to IRS.
There are two separate sets of obligations and relationships (1)Your obligation to IRS and your business relationship with the tax preparer, and (2) the other person's relationship with the tax preparer and his obligation to IRS ...
The two should not be commingled.
You need to force the tax preparer to be accountable here ... rather than the preparer taking the path of least resistance by forcing a relationship that SHOULDN'T exist ... between you and this other person.
Not only is this a breach of client confidentiality, the preparer is shirking their professional responsibiity.
Let me know if you have questions ...