The man seated to Queen Emma's right might be Duke Paul Friedrich of Mecklenburg-Schwerin, who was after the death of Friedrich Franz III. the eldest surviving half-brother of the groom, brother of Grand Duchess Vladimir, and uncle of the young Grand Duke of Mecklenburg-Schwerin who is seated to Queen Emma's left.
If so, the lady to his right with the impressive tiara should be his wife Duchess Marie, née Princess Windisch-Graetz.