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

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)