In case the idea of rural aristocracy could be missed, the artist, Mr. Charles Philips, placed a sheep almost in the middle of the group.
The man in the center is probably Charles Watson-Wentworth, 2nd Marquess of Rockingham, styled The Hon. Charles Watson-Wentworth before 1733, Viscount Higham between 1733 and 1746, Earl of Malton between 1746 and 1750, and The Marquess of Rockingham in 1750. He served as PM twice. He died of influenza during his second term. He was dealing with the close of the American Revolution at the time. He died without issue. The Lady beside him might be Mary Bright or Mary Liddell. Wikipedia states he married Mary Bright while thepeerage states he married Mary Liddell.
The older man wearing the order sash and order star may be his father, Thomas Watson-Wentworth, 1st Marquess of Rockingham. He married Lady Mary Finch who cannot be identified here (see Mary Bright’s image for an explanation). They had one son, seen here, and two daughters, probably seen here. Mary Finch’s father, Daniel Finch, 7th Earl of Winchilsea, had many children of both genders, some of whom can probably be seen here. I hope I got this straight.
The young man in green appears to have a five o’clock shadow.
From Wikimedia. The original has numerous spots throughout that were removed with Photoshop. Many spots were in the seams between stones, the shadows cast by moldings, and other darker structural features. The group was excerpted with Photoshop and the size was then doubled so this image has a height of 126.75 cm at a resolution of 24.41 pixels/cm (62 pixels per inch). Also posted to the Reign of Louis XV 1715 - 1774 Album here.