Daughter has son, 8, New BF has Hep C-PLEASE HELP !!!

My 40 yr old daughter lived with an IV drug user for 7 mos who she found out has Hep C. She has an 8 yr old son, never said one word about caring if
HE would get it, just said, "Oh, well; I probably have it now anyway."
Things with them got really bad drug wise and she gave temporary custody of the boy to her sister, 36, with whom she has never gotten along. Her sister is a perfectionist, looks like a Barbie doll and has a good job. She also has a husband and 2 children 7 and 4. So all has gone nicely for 2 weeks there for my GSon. Well, today I remembered that her sister's BF has Hep c and I FORGOT TO TELL MY DAUGHTER THIS. She is going to raise the roof and have a total fit. Thinking I've exposed her family to HepC. I read that sharing toothbrushes is the easiest way to get it.
I can't sleep, I'm depressed, I can't tell her; I'm asking my husband to tell her. She'll dump him; we'll have to raise him and we're 65; it isn't even my husband's grandson. He doesnt want to raise anyone's kids. I am NOT PUTTING HIM IN FOSTER CARE, PERIOD. She is furious because she had to pick him up at school today, missing work, he has a stomachache, fever and
headache. He had a major cry , just traumatic, over his mom last night and has nightmares every night. He Hates his mom's BFriend an iv drug user for 21 years. HIs life with my younger daughter has been a Fairytale; a Wonderland of Childhood w/his very first parties, sunday school, no drugs around and all new clothes. Someone please help me!!!!!I am so depressed!!!!