RE: Identifying uniform jacket of groom.
He is wearing a military-style uniform based on the cut and style of the jacket. Specifically, the wide cuffs on the sleeves with piping along the edge, the simple epaulets on the shoulders with two bars are each indicating a rank, and the raised collar also with a piping along the edge. However, I am inclined to say it is not actual military (army) and is certainly not part of the Polish Blue Army that fought the Russians. I would say he may be wearing some form of police uniform or possibly some other government agency uniform. I downloaded the imaged and adjusted the contrasts and brightness, but that helped only slightly in bringing out a few more details. For instance, the lower (skirt) part of the jacket is buttoned. That would allow the person to unfasten them to be able to mount and ride a horse. I never saw this feature on a military uniform of that period. I hope this helps.