In my experience, anyone involved in a life insurance beneficiary dispute should hire an attorney as soon as possible. The attorney can then formally notify the insurance company of the legal and factual basis for the claim.
The importance is highlighted by a very recent federal district court opinion from Houston. In Harmon v. Harmon, the insured's widow challenged a designation in favor of the insured's daughter. The widow claimed the designation was procured by fraud, deception, and at a point when the insured was incompetent to make the designation due to lack of mental capacity.
Unfortunately, it does not appear the widow retained an attorney to write a letter to the insurance company before it paid the benefits to the daughter. Instead, the widow claimed she called the insurance company to inform it of the dispute. She then went to court and sued the insurance company and the daughter. She lost.
There is a chance the result could have been different had she hired an attorney in Texas to write a letter formally notifying the insurance company of the dispute. Instead, she put the insurance company in the position of defending its decision to pay the daughter.