G. A. Henty 
Through Russian Snows / A Story of Napoleon’s Retreat from Moscow [EPUB ebook] 

Henty gives us two brothers as heroes, Frank and Julian Wyatt from Weymouth. Julian, through some fault of his own, is carried to France by smugglers and ends up in a French prison. Given the opportunity to fight for France in Germany, Julian agrees and is off to the invasion of Russia. Brother Frank obtains a commission in the army in England, learns Russian, fights a duel, and is sent on detached service to Russia as aide-de-camp to Sir Robert Wilson. (Excerpt from Goodreads)