All that can presently (July 2023) be gleaned about The Sisters Cuthbert from sheet music covers and by Internet searching is that they were presumably English music hall performers active in the 1880s. Contemporary playbills describe them as Charming Duettists and Dancers. They have been featured on at least 2 works published in 1881.
Their portrait on the left is taken from Happy Eliza and Converted Jane (1881) words & music by Will Oliver, and published by Alphonse Bertini & Co., London, England. This work was also their signature tune.
Surfers are welcome to contribute any further information about these performers.

This list is derived from information provided by Monologues.co.uk which went down sometime in 2023.
The loss of this valuable resource is very sad and a mystery.