No need to jump to conclusions. Their hygiene is obviously going to play a role but there is no reason to assume you'll be sick. You could have been in the bathroom with her while she was vomiting and still not get sick. Best thing to do is remind yourself that whatever is going to happen will happen. You have no control over it at this point. If you do get sick, you're totally going to make it through! Look at your grandmother, she's probably feeling much better now within a matter of days. Did your grandfather even catch it? He lives with her, surely his chances would have been a bit higher to catch it. If it happens, it happens! You'll get through it! You've totally got this and are so capable! I believe in you, try to believe in yourself!