Final answer:
The twin concerns when related lawyers represent both parties in the same matter are conflict of interest and lack of impartiality.
Step-by-step explanation:
When related lawyers represent both parties in the same matter, the twin concerns are conflict of interest and lack of impartiality. By representing both parties, the lawyer may face difficulties in providing unbiased advice and advocating vigorously for each client's best interests. This can compromise the lawyer's ability to fulfill their duty of loyalty and diligent representation to each client.
An example of this conflict of interest can be found in the case of Glasser v. United States (315 U.S. 60, 1942), where the simultaneous representation of co-defendants by a defense lawyer was found to violate the Assistance of Counsel Clause of the Sixth Amendment.
To avoid these concerns, lawyers have an ethical duty to avoid conflicts of interest and maintain the trust and confidentiality of client information. They should only represent parties with conflicting interests if all parties are fully informed and provide their informed consent, or they should withdraw from representing one or both parties to protect the interests of each individual.