Hello again, and welcome back to JustAnswer.
Your best course of action would be to bring this ring to a jeweler in your area who may specialize in handmade designs, if you prefer to have your bride's and groom's new rings uniquely designed and not choose something already made. Only a jeweler who can examine the ring you wish to trade in, in person, in order to exchange it for the two new rings, will be able to give you a price s/he would value it at, and explain more about what you might be able to choose, from an existing collection, or have handcrafted for the bride's and groom's rings. Also, please keep in mind that the insurance appraisal value is much higher than what a jeweler would actually give you for the ring.
You'll need to decide, after the jeweler (and you can comparison shop, in several jewelry stores) tells you how much you have to spend, based upon what they'll give you for the ring, whether you want to basically 'trade' it for the two new rings, or if you would like to use some of the diamonds and/or platinum from the original ring in the new ones. That decision will affect the price and/or negotiations.
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I wish you much good luck!
Edited by Cher on 4/21/2010 at 3:07 AM EST