I haven't read any of the other answers yet.
Will say just a few things off the top of my head.
First . . . it sounds like MIL/grandma WAS in fact,
taking good care of your 10-year-old for a while.
Given your promise not to make him switch schools again,
I wonder if he could stay w/grandma . . . if only until the winter break,
separate from what the rest of you do, perhaps even through until
next summer. ???
Consider having a conversation w/your 10-year-old
about the overall situation. See what he thinks.
Tell him that you/Mom will make the ultimate decision
but that you want his opinion/needs included
in your decision-making process.
That you expecially don't want to short-change him
because of all the crazyness going on in the family.
Next . . . . it sounds like YOUR mom was a good resource
when the new baby was brand new.
Can you and the baby and the 2-year-old go back to YOUR mom's home,
at least for a few months, to help you get back on your feet.
I'm guessing that maternal grandma would probably be better
at childproofing as well as supporting you in baby care.
You've already found that counseling with DH didn't work well,
if at all. It's good that you continued counseling yourself.
Probably gave you some helpful tools and techniques
to keep yourself functioning through the last few months.
So . . . . given your own sanity and wellbeing as #1 priority,
and then best situation for the children as #2 priority,
if it were me in this situation, I think I'd go to my mom's home,
at least for a while, taking the two younger children with you.
Set a time deadline for yourself to reconsider your options,
after you've had at least a few weeks of (relative) calm, w/Mom.
Thank you for sharing your family saga with us.
In addition to your ability to describe the situation clearly,
I think you have given many of us some perspective
and an opportunity to appreciate our own circumstances,
which are likely far less complicated than your own.
Wishing you well, and the strength
to take care of yourself and your children.
====================================
I don't know whether this is an option in your location.
However . . . . there are match-making organizations/cooperatives
where moms with kids connect with other moms with kids
and combine households. Their attitudes about child-rearing
and other needs have to be in sync with one another.
I would hate to see you have to go back to work
while your youngest is still a baby.
And, in fact, while your middle child isn't yet in school.
Part of your husband's difficulty may in fact
relate to his hour-long commute every day.
I am not excusing his behavior.
He just may be in over his head
regarding his own competence and motivation.
I just flashed on a fantasy scenario.
A mediation, facilitated by a competent professional,
in which the parties included your parents,
your DH's mom, you and DH, and your 10-year-old.
No yelling allowed.