I read an introduction to S&S which reminded the reader that "The Old Gentleman" can mean the devil. I think the 'devil' here may not be just the general wish to preserve an estate, and leave most of the money to that heir to keep the estate together, but real worries about the financial future. In the time of the novel, there was high inflation.* To keep the estate together might require larger and larger sums. So, the 'old gentlemen' may have impoverished his nieces by acting on his fears and uncertainties about keeping Norland together. I'm not defending it, just saying it's something interesting to bear in mind while reading. People's views and comments about money are something I will pay particular attention to in this read.