Oh mama, you are so frazzled!
Gentle discipline does NOT equal 'mom is a doormat'.
It sounds like you've been treated like a doormat...and you have to set and enforce some boundaries for yourself to feel (and be) respected.
1. Pick a night and that's mom's night out. Start today. When DH gets in the door, say to him: Dinner is either leftovers or sandwiches. I am leaving for the evening so I can recharge and be a good wife and mother. I will be back at bedtime. Don't leave for an HOUR...leave for four. Your kids are ALL old enough to be with dad for four hours. Drive around, go wander the mall, go sit at a bakery and eat pastries, go to a bookstore, go get coffee, call a girlfriend and go b!tch about this insanity. But GET OUT and GO DO something that has NOTHING to do with your children or husband. Don't answer the cell phone if he calls. JUST GET OUT. Repeat weekly. When baby arrives, take baby with you until baby can be with dad for an hour. Then continue. No negotiations, no arguments. Just YOU making YOU a priority.
2. Regarding homeschooling. When I was pregnant with #4, homeschooling slid. A LOT. Cut yourself some slack and don't sweat it. Network with some area homeschoolers and see if you can find a few classes or playgroups for the kids. At home, hit the library and borrow some educational videos from there. But relax. It will all be ok.
3. Regarding gentle discipline of the kids. Pick ONE area of the house per day. During everyone's "Best Time" (ours is late morning, after snack but before lunch) announce that it is clean up time in this area, and we are all working together as a family to get it done. Period. they can take as long as they'd like, but it needs to get done before ANYTHING ELSE happens. Break for lunch if need be, but tackle it. Let them throw whatever fit they want, but stick with it. They will do it...it might take a bit of perserverance on your part, but don't beg/ask/plead/negotiate. You are all a family and they need to pull together when mom is having a hard time. When the room is done, play with your kids for a little while. Hide and seek is silly, easy, and fun...even when pregnant. So is playdough. Or making cookies. But make time for some fun.
4. Consider adding some MILD structure to the day. You can't go from unstructured to structured and back...that's inconsistent and kids aren't knowing what to expect. Also, don't plan on anything 'working' instantly. It took days/months/years for things to get this out of hand, it isn't going to snap into place in a week. However, you CAN let the oldest know they need to help play with the middle two while you and the youngest take a nap. YOU need the rest, and I'm sure the 2yo could use the snuggles. When you get up from the nap, relieve the 9yo of the younger kids and get everyone a snack while the 9yo works on something educational of their choosing. While the littles are eating, go spend a few minutes paying attention to the 9yo. I know it's a juggling act, but that's the way it goes when we've got lots of kids running hither and yon.
Keep venting, talking, etc here. We all understand how you feel. You are a capable, caring, and loving mama who wants the best for your kids and family. You are giving so much to them that you aren't making yourself the priority. That makes being a mama SO hard. Look in the mirror and remind yourself you ARE an invaluable resource to your family. Clearly they believe they can't live without you!