Partner with cancer is verbally abusice

Been there.  Done that.  Trust me when I say I have personally experienced this.  Here is my advice based on what you wrote.

1.  "It doesn't help that I am tired and cranky working 70 hours per week, taking care of our 2 kids, and trying to be there for her."

Your taking on too much.  I did this as well.  I work in the tax field and when its tax season, we work and take on as many clients
as we can.  I know what its like to work 70 hours per week or more.  But you got to slow down because if your taking on the role of
caregiver, raising 2 kids, and workaholic, then a crash is coming soon.  You have to get someone at the office to take on more work
and you take on less.  Caregivers get burned out.   Something has to give and hopefully its work at the office.

As a side note, my wife came home from the hospital after the birth of our 3rd child and literally went to live in the basement.  It
took 2 years before my wife's sister came to visit and got her to go to a clinic where she was eventually diagnosed with cancer. So I know
what your going through.  You the caregiver have to start going to the gym, eating healthy every day and taking care of yourself.  Take
time off for yourself.

2. "I am not always a saint, and my tone is not that of an angel, when I get fed up with how she acts I tell her directly that she needs to
change her ways and how crazy she is."

Arguing with someone who is crazy is pointless.  I dont blame you for getting mad but I learned from experience that getting upset
with someone who is really crazy angry took away from my health.  And I stopped arguing with my wife.  I argue with other people, I
debate other people and am passionate about many issues, but I completely stopped arguing with my wife at least 5 years ago.  It
was pointless.  I gained nothing but felt less energetic and less about myself.  I think you have to find the caregiver path where you are
healthy and you are being taken care of.  Otherwise, you will go nuts.  Start going to the gym and eat healthy every day and take breaks.
Can you go on a 3-day vacation with the kids somewhere?  I take vacations with the kids often and I love it. 

3. "She also rely's on her mom a little too much and I feel ganged up on a lot of the time by the 2 of them."

My wife's family hated me for years (and they still might hate me for all I know).  But over time, they have seen my wife's
bad behavior and are nicer to me.  My wife's sister is a friend and she talks to me often to see how I am doing.  I think in time
your in-laws will appreciate you but in the beginning stages, there is distrust everywhere.  In time, the truth will reveal itself but it
takes time.

4. "I am worn out. I keep trying to pray thru it but I'm losing my mind."

You have to take breaks and take care of yourself.  You have to really study your schedule and see where you can change your
time and schedule to benefit you.