OK, breathe... Obviously not a skill taught at home (sympathy, not sarcasm) so let's do this together: Breathe in filling top, middle then bottom of lungs 'til you're about to burst - hold, 2, 3, 4; and slowly let the air out. Repeat at least twice.
Mom is not being fair, but I don't know if you have the power to do anything about that.

Consider, during a moment of relative calm, saying something like; "Mom, I really am looking forward to this trip and your part in the trip for me. I ask that you please try very hard, regardless of step-dad, to be able to come on this trip for me. I will go regardless, but it will be a much better trip if you can join me." I don't know if that's the kind of request that would soften or anger your mom - you've got to figure out that one.
I find that driving from even farther away than 10 hours is shorter and less stressful than the process of flying. I realize that 10 hours on your own would be less than ideal; but if you can break up the drive or do other things to make the drive safely - do so. Don't give up because others are being difficult. We stop regularly on our drives to FL to stretch our legs and change the music/book-on-CD at rest areas along the drive. We also take ourselves a nice picnic lunch and try to find either a rest area with nice picnic tables or a city park not far off our route. Just ideas...
Finally, we aren't getting to MK 'til 6:30 p.m. on the 20th and we plan to have a great time. Our strategy is to enjoy some of the entertainment that is unique to the holidays or will have a holiday flair (Dapper Dans, Celebrate the Season, Frozen Holiday Wish) and we are going to try to ride BTMRR during the fireworks. If we are in-line or just off the ride for fireworks, that's OK too - it will be an interesting view either way. We expect to fit the Jingle Jungle Cruise in between the castle lighting (Frozen Holiday Wish) and going to BTMRR. It might not be a lot of rides, but I think we will get a lot of holiday atmosphere for our time and it will really set a good tone for our trip. If you can stay up late then you should get your other mountains in after fireworks without much or a problem. I've heard you can even get on 7DMT late at night! Remember that late at night the posted wait times are often inflated and that you only have to be in line before park closing not off the ride by park closing. I don't know exactly what your priorities are, but I hope you can find a strategy that works for your preferences.
As far as dining, one of our must-do TS ADRs is right there at your resort - The Wave is fabulous and we consider it a hidden gem - look at the menus and see if anything there makes your mouth water. We think it's a special experience at a good price/value. We also have both a breakfast ADR and a lunch ADR a mono-rail ride away from you at Kona Cafe. Often, we enjoy a hearty late breakfast or a lunch much better than a dinner when we are either tired after a day of touring or anxious to get to evening touring - and there is more availability and cheaper pricing at those times!
It's hard not to get discouraged when it feels like things keep smacking you in the head

, but try some of the ideas here in this and other posts

to pick yourself up and keep on planning. Soon you will be enjoying the amazing holiday atmosphere that is only found at Disney

and the difficulties you faced to get to the magic will be a fading memory.