The remains of Laci Peterson, eight months pregnant when she disappeared last Christmas Eve, were found along San Francisco Bay, in April.
Scott Peterson has pleaded innocent to her killing and is currently awaiting trial.
The Petesons wrote to the Rochas, Laci's parents, asking that they delay the funerals of Laci and her unborn son, until "such time Scott is exonerated and we all join together as a family to mourn your daughter, Scott's wife, our and your grandson and Scott's son who has been taken from all of us so cruelly."
The Rocha family held a funeral, where Laci Peterson and her son who were buried together in the same casket, last week in a private service. The Petersons said they learned of the funeral via news reports.
According to ABC affiliate KTVU-TV, the Petersons received an e-mail from the Rochas' lawyer, Adam Stewart that said: "You have been aware for several months that our firm represents the interests of the Rocha family. Despite this, you continue to contact members of the family via e-mail, mail and telephone. We ask that you discontinue this practice immediately. The family wishes to be left alone during this difficult time."