My heart goes out to your family in such a difficult situation...I will join you all in the hope of a calm, quiet passing...
I would urge you before considering euthanasia to spend a good amount of time figuring out what KIND of "aggression" (I hate that word) kitty shows. When I took in my Hopey, she had been returned 3 times for "random" biting and bit at least 3 people in the shelter as well. Well, no wonder, she has severe cage rage, which no one bothered to figure out. She will attack strangers if they aren't clear with their actions and she is petting reactive as well. She has been with me since 2003 and it has been 2 years since she has tried to attack any member of my household....because we know what her triggers are and we don't press them. We give her lots of space and never enter a door way if she's sitting there, we ask her and give her the opportunity to move first. She never gets pet over the head, we let her smell our hand and then only give her pets around the chin, she likes it best there anyway
I never touch her bum. Ever.
Dumb Friends League has *amazing* articles about cat aggression, found on this page (it's now a PDF file) .
http://www.ddfl.org/sites/default/files/cathumag.pdf They taught me so much about cat behaviour when I took in Hopey who, by the way, now peacefully lives with 2 other cats and a dog, which I NEVER thought would happen, so there is hope, but you will have to be patient
I wish you luck and peace!!