A bit of background: I am executer of my brothers, and my mothers wills. Both have spoken to me about their wills wishes etc.
Brother has DD1 from his first marriage, and then DS1 and DD2 from second marriage (still married). He has recently informed me that he and his wife are leaving everything to DS1 and DD2 (so the kids from the second marriage) and nothing to DD1. The reasons for this are that DD1 is likely to inherit from her mother, and that as she isn't 2ndwifes daughter she shouldn't inherit from that relationship anyway.
My DM, who was also told, is really quite upset. She wants to change her will, so that instead of her leaving everything between me and DB, she would leave 1/6 to DD1 to make up for this.
I am very close to his DD1, and find DB's behaviour awful. But, can only see that if DM does this, it would cause a breakdown in mine and DB's relationship when she dies. I want to broach it with DB and explain his behaviour is out of order. I can't begin to imagine writing one of my children out of my will just because they had a different father. DB is unlikely to have more than about 50p to leave anyone, so it's not about the money it's about the principle!