If the soon-to-be husband and wife are concerned about their individual assets entering into the premarital agreement process — or even if they are uncomfortable having financial discussions directly — then the couple should choose to secure individual legal counsel and have the attorneys “negotiate” the document.
(Certainly the bar association would recommend this; that keeps the lawyers working!)
But for couples that can work together calmly and rationally, involving lawyers in the creation of a Premarital Agreement is not a requirement — nor is it “true” that a better legal agreement is created because multiple lawyers are involved.
A couple can certainly create their own prenuptial agreement on a pro se (self help) basis. See the details on Standard Legal’s Premarital Agreement legal forms software.