Hi, Rebecca!
Welcome to the Disney Parks Moms Panel! It sounds like you have an unforgettable vacation coming up in October!
With your schedule, I'd take a look at the
Disney World Park Hours calendar and make a decision. Based on the date you arrive, Magic Kingdom Park is open until 10PM. If you decide to go to the park once you get to Orlando, you'll have a pretty long day to play on Monday. If you decide to wait and use your short park day on Friday, the park that opens the earliest is also Magic Kingdom Park! If you are staying at a Disney resort, you can take advantage of an
Extra Magic Hour and start playing in the park on your last day at 8AM. I think you'll want to base your choice on if your family will have more fun staying up late or getting up early.
I know my family would want to take advantage of both choices! I hope that perspective helps you a bit in making the choice between Monday or Friday park time.
Feel free to come back to the Disney Parks Moms Panel anytime! I'll be here to answer more questions!
-Jen