I have children in 6th, 4th, 2nd, and preschool. I agree with a fellow post to only focus on math, reading, and handwriting during PK-2. I would also throw developing good character in there. If I manage to cover anything extra with them, great! If not, it's no big deal. We do art, science, and history together. The little ones sit in or are close by and participate in some of this. My children are all 2 years apart, so I combine some subjects like spelling. For example, I'm currently using All About Spelling with my 4th and 6th grader. This worked well because my 6th grader is weak in spelling and my 4th grader is strong. Both children are also doing grammar and writing together. Curriculum that's great for large families: Five In A Row and Konos both allow you to do art, history, science, geography, and some language arts all together as a family. Heart of Dakota, My Father's World, and Sonlight allow you to combine a few grades together. We are also big on project-based learning, where the kids choose a subject of interest. For example, during our last PBL, one child focused on fashion design, another on dinosaurs, another on the Statue of Liberty, and another focused on animals. I'm basically there to mentor, help them check out books or give suggestions, provide supplies, and drive them to a field trip (such as the Museum of Life and Science because they have a space and dinosaur exhibit), but they are in charge of how and what they learn. My kids have the most fun when we learn this way.
It's a big decision and homeschooling definitely is challenging, but so worth it. I wish you well in whatever you decide!