When you are in labor and giving birth, you don't want to have to be worrying about your toddler. You may think you will be worried about him being away from you, and maybe you will, but it may just be too stressful for you to have him there. I would keep your options open.
I think the plan to have your husband and doula there and prepare him for witnessing a homebirth is a good one, but I would also work on getting your son used to the doula or someone else (and make sure she knows she may be doing babysitting duty rather than labor support), and understand he may have to leave for his sake or your own.
My sensitive ds did fine at his brother's birth... but, he had grandma there holding him the whole time, and the birth went really fast so he was not watching me labor for hours (he was awake for probably only the last 20 minutes). He also came with me to every mw appt, and was used to "helping" our mw with measuring (he loved using the measuring tape), etc. With this one, we will play it by ear. The boys may both be there, but it will depend on timing and circumstance.
Melissa , wife to Tom , mom to The Baron , the Bean , Little Bear , and Baby Beaver