I think it is quite obvious that JA/ON did not greatly approve of Lady Middleton. Sir John was stupid and inelegant, and he was wholly absorbed in sport, he was so "sociabe" that any company, however stupid, was better to him than being alone, but he had a certain warmth and good-nature that was missing in his wife. Her only real emotion seems to be for her children and it's quite obvious that JA did not approve of them being so spoiled and badly behaved. I think that her opinion of hte Middletons esp Lady M -is much teh same as Elinor Dashwood's.. that they are basically decent enough - even lady M is polite and considerate up to a point - but they are so stupid and egotistical that they are not people Elinor could really have a freindship with, but she's polite and pleasant to them and shows gratitude for the kindnesses that they do bestow on her and her family. However they are not really interesting company...Marianne doesn't even show or feel much gratitude to them..