As a mother of three who just moved from MN, I can completely understand your situation. It is a long drive and you will most likely get tired no matter what you bring. But its okay, seeing family and taking a trip is worth it.
Since your kids are young, it will be hard to completely keep them entertained. Kids that age don't do a lot by themselves. But you know what your 2 year old is capable of doing. If he likes to draw, then a magnadoodle-type toy would be great, especially if the writing utensil is attached. (My kids always seemed to drop their crayons, chalk, etc.) For lots of ideas for travel games you can visit www.nickjr.com; they have a section on car travel activities and you can sort by age.
A big help for my family on our long trips was making sure to get the kids out at the travel plazas, unless they were sleeping of course. But otherwise, we always got them out of their car seats and had "wiggle" time. We would play games like "run from that tree to the building", Race Daddy to the door or Follow the Leader. It takes extra time, but helps a lot.
We also brought a shoe box full of activities that could be played without a parent watching. Like Little People, Duplo Legos, McD's Toddler Toys, etc. We made sure to only bring out one new thing at a time and space them out throughout the journey. The trip is 18 hours of driving, you add in stops and hotel time it can get to be 30 hrs before you're done.
If you have a large enough vehicle, you could schedule time for a parent to sit by the kids. With a parent right there, my kids didn't need toys because we would see things out the window and talk about the trip. With both you and your husband, you could take turns driving, take turns with the kids, and have parent talk time. (No doubt this trip could be quality time for you and your husband too.)
Since this is a family trip, I would suggest finding pictures of who you will be seeing on the trip and putting an album together. Any way that you can prepare your kids for the faces they will see, may help once you arrive.
Car friendly snacks are good. I set out what was okay while moving and what was "only when we stopped" food. I had a cooler with: apple slices in ziploc bags with a bit of lemon juice to keep them from going brown, baby carrots, juice/flavored water bags with straws, cans of soda pop for parents, sandwich supplies, etc. I also had dry foods like crackers, bananas, pretzels, and peanut butter with disposable spoons. You could also hard boil some eggs if your son likes those. There are plenty of options.
I made sure to bring the diaper bag plus a box in the car to refill the diaper bag as needed. Plus the pack and play for at the hotel, and an overnight bag just for the travel time so you don't have to unload all your vacation stuff just for one night.
You will want to plan ahead too about overnight options. When we made the journey the first time, our kids slept so much in the car we knew if we stopped at a hotel they wouldn't sleep much so we opted to drive as much as we could as far as we could. The second time we made the journey, we planned when to stop and made sure to keep the kids awake the last number of hours prior to our stop for the night.
This is becoming a novel. If you would appreciate more thoughts or if you have questions, please send me a message. I hope you have a great trip.