This all sounds very odd to me.
If I have understood you correctly your second daughter is on good terms with her aunt, your sister, and with one of her own sisters. If this is so, surely one of the two can exxplain exactly what is going on.
I realise your eldest daughter has said her sister was offended when you moved some years ago, but that cannot surely be the only thing.
Two years is a long time to neither hear from nor see a daughter.
Are you and your husband at odds about this? I am puzzled why he still helps this daughter out with money (which I am guessing is never returned) and legal advice, even although she had not the decency to get in touch when her father was diagnosed with cancer.
Did she actually know about his illness? And if so, how - through her sisters or aunt or what?
Where is your younger daughter in all this?
Hope you don't feel these questions are impertinent, but you have left so much out that it is difficult to advise you.
In your place, I would start by discussing this problem with your husband and try to work out what you both think you should do,
Then ask her for an explanation if you haven't already done so, or try to get a reasonable explanation from one of the members of the family this woman actually talks to.
I would also stop sending money, gifts, cards, e-mails or phoning her, as she obviously wants no contact with you.
It must be hard when you have no idea what you did or said, but if she will not explain then I am afraid you will have to just accept that there is no contact between you.