[Седой]

Here's a little thing for many years now I see hanging on the wall in a house of Odessa . Acquired , most likely, even in the 20s of last century. Gouache (or temperature ? ) 28h44 cm, tightly packed in a wide mat of thick and durable pre-revolutionary cardboard.
Size of mat and frame - 55 cm h71

 I would like to know:
a) Is it ( with a sufficiently high degree of probability ), the work Harlampy Dmitrievich Kostandi , as the signature " H.Kostandi " in the lower right corner?
b) what kind of artistic and material value may be , if the author is confirmed ?