The belt buckles appear to have crossed rifles or crossed sabers looks like what the Army Infantry or Calvary would use.  They do not look, to me, to be crossed cannons.  If they were Marines, wouldn't the insignia include the globe & anchor?

The barrels appears to be not long enough to be a trapdoor rifle & the stock too long to be a carbine.

I don't see any bayonets hanging from belts.  That would be expected if the arms are some type of carbine.  The Lee Navy bayonet scabbard had wire hooks to fit in eyelets.  The belts shown could be for the Lee Navy.  The Lee rifle had a pistol grip and I do not see any in the photo although it is difficult to tell.    (You need to Login

To me, the rifles apprear not to be either Krags or trapdoors.  I'd have to guess they are Lee Navy rifles.