Possible mold in parents bathroom, any advice?

Hi everyone,

I came to visit my parents today, and found a wonderful surprise in their bathroom. What appears to be mold is growing all over the ceiling. So, as someone who has never dealt with this...

1) How bad does this look?

2) The bathroom is quite small, does not have a ventilation fan. Is this likely the cause of the mold growing?

3) What exactly do I need to do here? Is this something I could take care of on my own? What sort of professional am I looking for, and (roughly) how much will a fix cost?

Pictures --> http://imgur.com/a/rdCa8