My mom was diagnosed with pancreatic cancer

I just finished my sophomore year of college and a week after I came home from school for the beginning of summer, my mom was diagnosed with pancreatic cancer. She is currently elligible for surgery in August. My question is, I have three younger sisters, ages 18, 16, and 12. The 18-year-old is supposed to start college out of state in the fall. I go to an out of state school as well. I have been helping my parents out a lot by making meals for the family each night and doing extra chores since I haven't been in school or working. My sisters finish school this week. My plan was to leave for summer school at my college in a week. However, I overheard my mom and dad talking saying how much of a help I've been already and how great it would be if I stayed here this summer while my mom starts chemo. Her surgery is supposed to happen in August if all goes well. I would return home from summer school on August 9.

I really want to do what is best for my family, and I was thinking that they might need my help more in the fall. I could take a semester off and possibly work a little/take a community college class or two/work on a novel I've had ideas for for a while now, along with helping out my mom of course (keep her company when my dad is at work and sisters are at school, cleaning, driving my sisters, and cooking).

I took the first semester of organic chemistry in the spring and I would like to take the second semester while it is fresh in my mind this summer (for 8 weeks). I like school a lot but I can't stand the thought of being so far away during such a hard time. My parents are telling me I need to make my own decision about summer since going back to school for summer isn't manditory, but here is my struggle-- this situation is so fresh and will take a lot of adjusting. My 16-year-old sister is my best friend in the world, and is being strong for my mom but also taking the news very hard. Would it be better to stay home to support my family in the beginning (right now) during her 8 weeks of chemo? Or would it be better to take time off in the fall when she has her surgery and will be continuing chemo and my sisters will be in school? Or... should I just plan on taking a lot of time off (summer and then possibly fall) to help the fam? Or, would it be best to stay in the summer and go back to school in the fall? I just have a feeling that fall semester would be so hard for me no matter what and my grades may be affected. I would rather take that chem class while it is fresh in my mind. I am thinking my best decision is to take off for a semester in fall, but after hearing my parents say they would love it if I were here this summer it just makes me feel so guilty to leave.