You have challenging questions. What are you going to do with the rest of your life? And, in addition, your parents are asking for immediate answers. This is not easy. However, here are some comments from experience that I hope will be helpful to you.
You should probably pick the major that is most interesting to you. Ideally, there will be one professor that will inspire you to choose the best major for you. If not, then think about what you would be doing in a potential job. Do you prefer working with people or doing research independently? Hopefully you will be interested enough in one of your classes to confirm your major within the next year.
What are you doing this summer? If you have time, then contact individuals who have careers in Marine Science, Microbiology, Genetics, and Plant Sciences. Visit them at work and see what they do. You will be absolutely amazed at what is involved in the day-to-day routine. This will help you confirm you are on the right track or that you need to change immediately. Whatever your career will be, you will be doing it every day for many years, so you need to make sure you are going to like it.
Your choice of careers will be in the academic world government lab, or in industry. You can have a very rewarding career in any of these areas. In academics, you would be doing research and teaching. In government, you would do research, surveillance monitoring, administration, or perhaps become involved in developing government policy. You seem to be thinking about an academic path, which is good, but I would also encourage you to consider industry, as these careers are sometimes more profitable. With a degree in any of the fields you are considering, in a private company, you could do research, marketing, sales, manufacturing, quality control, business development, or perhaps start your own company. At the company that I work for, the combination of a PhD degree with a career in sales seems to be most profitable. Since you are in Delaware, try looking for the job postings at DuPont (search for DuPont career paths). That will give you an idea about the local career potential in an industrial setting. Please note that there are always a lot of positions open in engineering, so if you have any aptitude or interest in engineering, you should consider this possibility for a career. Engineers are always in demand.
I would encourage you to get the highest degree possible, so a PhD is an excellent goal. However, it is much too early to worry about who will fund your PhD research. By the time you are ready for that step, you will already have an answer, or you will have switched to an MBA program, a teaching credential program, or applied for medical or law school. For now, just concentrate on confirming your current combination of majors and minors based on your personal preference.
To respond to your parents, I think they would be less worried if you had a definite goal. They may be worried because you haven’t been able to make up your mind on what to do. So tell them what you are planning to do to help make a final decision. Based on your research about local jobs, tell them about all of the career possibilities available to you. Hopefully, this will reassure them. They have invested a lot of effort in your success and they are asking questions because they are concerned about your future.