In Eberron during "The Last War" House Deneith, like all dragonmarked houses, remained neutral and sold their services to the highest bidders. But as mercenaries/soldiers this could lead to some unique problems.
One of which is: what would happen if two opposing countries both had House Deneith soldiers they'd hired opposing each other on the same battlefield? Would the House Deneith mercenaries fight their kindred on the opposite side or did they have some contractual limitations to their services that excluded such a possibility?
Was this situation ever addressed in any official material?