Your phobia does not define who you are! You are not a bad person!
I am so sorry about your grandmother.
I cannot give you advice on visiting your grandmother...I haven't been in that situation. However, as far as having children, I can totally relate.
I was worried about v'ing during pregnancy. I didn't though. I've had 3 children and I haven't v'd once during pregnancy.
Also, as far as them v'ing...I am able to care for them when they are sick. In fact, I am usually THE one that cares for them when they are sick. Honestly, I rarely catch anything they are sick with. Do I still worry about it? Yes. But, I am still able to be their mother and care for them.
I never caught anything in college. And I was NOT careful at all like I am now. I had 1 roommate my first year and 3 roommates the other years (we had an apartment). Enjoy it and try not to worry!