Hi Ron, welcome! Your kids are so very young right now, i wouldn't worry too much about having them sit much.
If standing works for you, it might help to have a high table with stools for them to sit on. That way you can stand up straight while they are doing sit work.
My kids got to go to a one room school house and one of the reasons it works so well is because the older kids get to practice what they've learned by overseeing the practice of the younger ones. Don't over-use the oldest but once they learn a skill you might encourage them to teach it to the next one.
There are curriculums that do almost, if not all, of the work for you but if you enjoy teaching you may not like those.
They work well in a pinch, tho'.
I'd make sure those little guys got out to play ball and dig up worms, too!