Lord Ravenshaw is either an earl, viscount, or a baron (as he is called "the Right Honourable") who owns Ecclesford, in Cornwall, where John Yates was staying before coming to Mansfield Park. Since there is a governess, it can be assumed Lord Ravenshaw has children.
In the party's performance of Lovers' Vows, Lord Ravenshaw played Baron Wildenhaim, but Yates believed he was unequal to the role and describes him as "a little man with a weak voice, always hoarse after ten minutes." Besides Yates, the other actors included Lord Ravenshaw's wife Lady Ravenshaw, the Duke, and Sir Henry.
Lord Ravenshaw ended the party two days before their performance, however, when his grandmother the dowager died. Yates and the other guests didn't want to put a stop to the play for an old woman who died two hundred miles away, but Lord Ravenshaw, who is "one of the most correct men in England," insisted.