Anita Petrovski, in his article "The Lesson of Piano - Femininity According to Giovanni Boldini" writes about the photographic qualities of these two paintings. The older woman, I don't think is ever identified, but the woman on the right is of Alice Guerin playing a duet in a more conventional pose; but even here, Boldini paints this stunning beauty (and by all accounts she was incredibly beautiful) with a deep décolletage of her dress and the exposed skin of her delicate shoulders.  

In the second painting (on the right) Boldini has her stretching from the concentration of playing. Though the stretch is a natural one, the pose is not. Instantly, the second painting is charged with intimacy.  The motion of her arms are abbreviated in a Boldini signature fashion of elongated flowing strokes. The hands of the older woman, however, are treated exactly the same as in the first. The subject of these two paintings, together, is unquestionably the beautiful Alice. This is quintessential French La Belle Époque style of female sensuality. 
(Anita Petrovski, universitas friburgensis juin 2002) 

It's a shame that these are the best images available on the net of these two. 
 

Paul César Helleu  
    
Rêverie (Daydream)    
1901 
(Alice wife of Paul Helleu) 
 
 

Notes 
 
 

• See more on Giovanni Boldini