This part from Ch. 21 always makes me wonder:

"In a morning's excursion to Exeter, they had met with two young ladies, whom Mrs. Jennings had the satisfaction of discovering to be her relations..."

I wonder how you could 'discover' someone to be related to you of whom you were previously completely unaware? We learn just after this that Lady Middleton had never seen them before in her life and has no idea if they are even genteel, so it seems there has been no contact whatsoever with them during all that time.

A bit later we read that 'it was painful for Sir John even to keep a third cousin to himself'. Third cousins would mean that their (Mrs. Jennings and the Steeles') grandparents were cousins?

How exactly, while shopping or doing whatever in Exeter, did this degree of relationship happen to even come up in conversation?

The other very suspicious thing is right after the above-quoted part about discovering they were related: "This was enough for Sir John to invite them directly to the Park, as soon as their present engagements at Exeter were over. Their engagements at Exeter instantly gave way before such an invitation."