Don Manuel Iturbe, envoy extraordinary and minister plenipotentiary, sits wearing the full civil uniform of an ambassador while the two attachés, Don Miguel Iturbe and Don Juan Beistegui, stand wearing lower grades of diplomatic dress.
All three wear the Order of St Stanislaus — the Polish royal order incorporated into the Romanov orders in 1832.
The records of the Mexican congress shows that Manuel Iturbe was authorised to accept Grand Cross of the order while Miguel (who I presume was Don Manuel’s son though I can’t confirm) and Juan Beistegui had to settle for the ordinary Cross of St Stanislaus.