My thoughts so far none of them favourable towards James and Mary:

Letter 29: The pictures, Most were to be given to James, except Cassandra's drawings and "the two pictures on tin..."but there seems to be a query as to who the French aricultural prints belonged to, "My Mother say the French agricultral Prints in the best bedroom were given were given by Edward to his two Sisters. Do you or he know anything about it?" Did James or Mary or both covert the Frendh prints as well as the other paintings?
Letter 30: JA declines an invitation to James and Mary's celebration at Ibthop, I too don't blame her. There is also the matter of "My father's old Ministers are alreasy deserting him to pay court to his son; (although I don't suppose that was James' fault or doing) the brown mare, which as well as the black was to devole to James at our removal, has not had the patience to wait for that & has settled herself even now at Deane.." Although JA seems to conceed that the death of Hugh Capet and Mr Skipsey (in La Faye's notes possibly James' horses)...has made the immediate possession of a Mare very convenient & everything else I suppose will be seized by degrees in the same manner." James or Mary or both impatiemt for the Austens to leave Seventon so they can take possession of the rectory?

I may be being rather harsh on James and Mary, we'll see.