Much more specific information is needed for a meaningful answer. It depends on what the client of attorney #2 is testifying about. If attorney #1 represents a businessman and attorney #2 represents that businessman's accountant, there would be no conflict about the accountant testifying on behalf of the businessman in a case against some unrelated party. If the accountant were asked to testify against the interest of the businessman and on behalf of an adverse party in attorney #1's case, there might well be a conflict for the law firm.
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Are the interests of individual 1 and individual 2 in conflict about this testimony? If so there appears to be a conflict of interest on the representation. Attorney 1 would not be able to question individual 2 adversely.
A definitive answer, if available, would depend on far more facts than you have given here.
Confidential information should not be disclosed in this Internet forum. I am a Wisconsin lawyer. The laws in each jurisdiction can be very different. I cannot give legal advice over the internet nor can I establish an attorney client relationship with you. You should NOT assume or otherwise conclude that there is an attorney -client relationship between any reader and this writer or his firm. These comments are only guideposts. They are not subject to any privilege protections. Indeed, these internet communications are neither privileged nor confidential. Accordingly, those using this form of communication need to be guarded in what they write. Because of the nature of these communications the information is general only and should not be relied upon in any specific case. This internet site is public forum, where the communications are not confidential or privileged. There may very well be merit to your defense or position in this type of situation. However, there are hardly sufficient details for an attorney to provide you with some path to follow. It is imperative that ALL of the facts in a particular situation be examined. No conclusion can be drawn from the communication that you have provided. There are some matters that are just better handled by an attorney familiar with the procedures of the courts in your area. Most, if not all, legal matters should not be handled via internet communication. At best, the responders on this site can give you a few hints and guidance. To deal with a legal problem, nothing is better than to consult with a lawyer who will give you some time and advice. If you cannot afford an attorney, there should be agencies in your area that can provide discounted, or even free, legal services.