A timely idea and, knowing Jenny Wilson, likely well-written plan. I've been in several situations of living with family members - with a sister and her children, and with a brother and his family. In both cases it would have been greatly beneficial to be able to declare as interdependent adults. The same is true when my partner and brought my my mum to live with us before she died. I expect there will come a time when we will take in and care for his sister who is in declining health. For all the ways in which we become family and support each other including financially, it is a great idea to recognize these bonds of commitment as being as valid as those formed through marriage.