The Sibling Problem

My grandfather was Gustav "Gust" Lange. He immigrated to Canada in 1911 after working for five years in Essen, Germany, to save money for his passage and send money back to his widowed mother and younger siblings. Gust was born 12 February 1888 (using the Gregorian calendar) in what is today known as Zamosty, Volyn', Ukraine, but at the time of his birth was in the Volhynia region of Russia.

This photograph was taken circa 1906 before Gust left home for German;
he is the oldest boy in a three-piece suit, holding a book in his left hand;
photograph from my personal collection

As you can see, the photo includes Gust, his mother, three sisters and three brothers. And that is the problem. The information from my Mom is that he had two sisters and four brothers.

Carl and Caroline (Ludwig) Lange

Frankly, none of the sons look to be only two years younger than Gust. And perhaps the infant, Fred, is not in the photograph, but that still doesn't explain the extra sister. Where to go from here?