Although Mozart composed more than 40 works labeled as sonatas for violin and piano, many of them belong to the juvenilia catalog and are virtually unrecognizable as sonatas in a modern sense. Rather, they are two movement fantasias for piano with violin obbligato, and the young savant even wrote “optional” in the score next to the fiddle part. Only when he journeyed into his 20s did Mozart begin to construct pieces that featured both instruments more equally. The first set of six such sonatas, known as the Palatinate because four of them were composed in Mannheim, the capital of this autonomous region, was unveiled in 1778.

This grouping has had something of a mini-revival in New York within the past year. Last fall, the siblings Gil and Orli Shaham performed three of the half-dozen in the main hall – now known as Stern Auditorium – at Carnegie. At that time, only Mr. Shaham’s large tone kept these delicate pieces from being swallowed by the cavernous environment. In the spring, five of the six were performed by violinist Mark Steinberg and pianist Mitsuko Uchida at Zankel Hall. Considering the disproportionate reliance on the keyboard, the result was essentially a piano recital, one where Ms. Uchida’s gossamer-like sound often had to compete with the more insistent rhythms of the nearby subway.

On Wednesday night, the Shaham duo performed the other three sonatas at the Kaplan Penthouse of Lincoln Center as the final entry in the “little night music” series. Finally, we had the proper setting for such diaphanous music, even if the cabaret seating was a bit unsettling.

Mr. Shaham is very well known, while his sister is still relatively obscure. That could change with time. A New Yorker, she is in line to become the first lady of this musical city: She is married to conductor David Robertson, the early favorite to succeed Lorin Maazel when that blessed day arrives for his retirement from the Philharmonic. For now, Ms. Shaham must content herself by holding the same position in St. Louis and appearing with her husband and his troubled ensemble at Carnegie Hall this coming season.

Shaham frere’s performance was excellent, bold, and modern. The gigantic tone of his 1699 “Countess Polignac” Stradivarius was almost too much for the room, but so enjoyable as to be an acceptable counterweight to the more meaty piano parts. In the K. 303 in C major, for example, his communicative skills carried the violin introduction far beyond the standard classical filigree, transforming the melodic line into a romantic narrative.

The only one of the six to presage the modern sonata is the K. 306. Not only does it consist of three movements, but the piano and violin parts are equally dramatic and expansive, which has led some scholars to believe that it was actually a sketch for a contemplated double concerto that never came to fruition. Perhaps the strongest argument for this theory is the 47-measure cadenza, which is primarily for keyboard but allows for some playful violinistic ornamentation.

But Orli Shaham is simply not capable of the same level of performance as Gil Shaham. There is no sugarcoated way to express this. I love my sister, too, but I don’t enlist her help in writing my reviews. This evening Ms. Shaham was tentative in the E flat major, less than acceptably accurate in the C major, and unsteady in her rhythmic drive in the bigger work – the D major. It would be comforting to think this was simply an off night, but I have heard this combination several times, and there is always a rather obvious disparity of technical skill.

The Mozart sonatas certainly are more difficult for the pianist than the violinist, and Mr. Shaham downplays the obstacles faced by the string player in an engaging and affable commentary. The Shahams present many differing repertoire choices, however, and there is always that pesky gap in skill. Gil would probably benefit immeasurably from a steadier accompanist, yet the duo is extremely familial – the Shahams even employed their older brother as their page-turner Wednesday evening.

Whatever they are doing, it works for them. There was a substantial line of fans before the concert hoping against hope for cancellations. The applause was not robust after each of the first two pieces, but this may simply have been a function of their extremely quiet endings. Certainly, there was a warm, sustained ovation at the conclusion, prompting the pair to offer up yet another of the six sonatas, preceded by Mr. Shaham’s promise that they would not indeed play all six.

Perhaps there are more important principles in the Shaham family than strict performance quality. Here’s to you, Mrs. Robertson. After all, no one ever came to hear Nannerl Mozart play.