The portrait is titled 'The Pilgrims' immediately beneath the print, and a pencilled caption in the margin identifies the individual sitters. These are: the Duke of St Albans, Colonel Tower, Henry, and the Hon. F. Howard.
I've seen another portrait from the same sitting, with the men posed in a different arrangement, and 'Henry was identified on that photograph as 'Lord Henry Gordon-Lennox'.
Comparison of the two portraits and their inscriptions suggests that the Duke of St Albans is the man seen here standing on the left, Colonel Tower is the man standing in the centre at the back, Lord Henry Gordon-Lennox is the seated man, and the man standing on the right is the Hon. F. Howard.
From an album compiled in the 1860s by a member of the Gordon-Lennox family.
Photographer unidentified.