The 1889 Annuaire de la Noblesse Russie, the definitive work published in St. Petersburg very clearly makes no mention of any Noble family called Dolgoruky. The Dolgorukov family, the subjject of this question, was a noble family of the highest ranks. If there was a branch called "Dolgoruky" it is from prior to 1650 and was of a far more minor nobility and thus can not be said to be the "same family".