Ordered that the order is affirmed insofar as appealed and cross-appealed from, without costs or disbursements.
"In an action to recover damages for legal malpractice, a plaintiff must demonstrate that the attorney `failed to exercise the ordinary reasonable skill and knowledge commonly possessed by a member of the legal profession' and that the attorney's breach of this duty proximately caused plaintiff to sustain actual and ascertainable damages . . . To establish causation, a plaintiff must show that he or she would have prevailed in the underlying action or would not have incurred any damages, but for the lawyer's negligence" ( Rudolf v Shayne, Dachs, Stanisci, Corker Sauer, 8 NY3d 438, 442 [citations omitted]). "For a defendant in a legal malpractice action to succeed on a motion for summary judgment, evidence must be submitted in admissible form establishing that the plaintiff is unable to prove at least one of [the] essential elements [of legal malpractice]" ( Shopsin v Siben Siben, 268 AD2d 578; see Ippolito v McCormack, Damiani, Lowe Mellon, 265 AD2d 303).
The defendant failed to prove his prima facie entitlement to judgment as a matter of law since he did not demonstrate that the plaintiffs are unable to prove one of the essential elements of their malpractice claim ( see Shopsin v Siben Siben, 268 AD2d 578). Similarly, the plaintiffs were not entitled to summary judgment since questions of fact exist regarding the malpractice claim ( see Avery v Sirlin, 26 AD3d 451; Maddux v Schur, 16 AD3d 873).
Accordingly, the Supreme Court properly denied the respective motions for summary judgment ( see Alvarez v Prospect Hosp., 68 NY2d 320).