DECISION ORDER
ORDERED that the order is reversed insofar as appealed from, on the law, with costs, and the mother's petitions for sole custody are granted.
The sole criterion in a custody case is the "best interests of the child and what will best promote [his or her] welfare and happiness" (Eschbach v. Eschbach, 56 N.Y.2d 167, 171; see Lincoln v. Lincoln, 24 N.Y.2d 270, 272; Prete v. Prete, 193 A.D.2d 804, 805). An award of joint custody is appropriate only where the parties involved are relatively stable, amicable parents who can behave in a mature, civilized fashion (see Braiman v. Braiman, 44 N.Y.2d 584, 589-590). Further, the parties "must be capable of cooperating in making decisions on matters relating to the care and welfare of the children" (Trolf v. Trolf, 126 A.D.2d 544).
It is well settled that this court's authority in custody determinations is as broad as that of the hearing court (see Matter of Louise E.S. v. W. Stephen S., 64 N.Y.2d 946, 947). Moreover, an appellate court may not allow a custody determination to stand where it lacks a sound and substantial basis in the record (see Coyne v. Coyne, 150 A.D.2d 573, 574; Skolnick v. Skolnick, 142 A.D.2d 570). While mindful of the hearing court's advantage in being able to observe the demeanor and assess the credibility of the witnesses (see Matter of Louise E.S. v. W. Stephen S., supra), nevertheless, the joint custody award cannot be justified on the basis of this record. Indeed, the evidence adduced at the hearing demonstrated that joint custody is not appropriate under the circumstances, and that the mother is the more fit custodian of the children.
Accordingly, the Family Court erred in denying the mother's petitions for sole custody.
SANTUCCI, J.P., ALTMAN, S. MILLER and McGINITY, JJ., concur.