Yeah, it's a shame, why do people feel the need to be petty and spitful...don't get it. I am so glad hubby is aware of it and doesn't fall for the manipulations. She had quite a bit of interference in her other sons life. one time she started gossip about them and i just said, well look, they had six kids, and stayed together, that tells me all I need to know. Anything else they can tell me themselves. I know gossip can be fun, but it kills three so...I just wish I understood better. Maybe I don't need to understand just avoid it whenever I can!
Usually, it's because of insecurity, but sometimes it's due to narcissism, most of the time, both. Bottom line is that it all goes back to how they've chosen to react to their own childhoods and upbringing, which you can't do anything about. So, you're right. Just keep doing what you're doing and avoid it when you can.