A., I have to say that I empathize completely with your situation (wanting to be near family, wanting to foster that wonderful bond between your kids and their grandparents). I also empathize with big life changes being difficult while the transition is taking place, so I feel for your husband, too.
Looking at the bigger picture, though, I have to say that if it were my husband, we'd definitely be having talks about sometimes having to do things for the greater good of the family. Why?
1) His relationship with his parents seems volatile (loving, but volatile!) from what you've said, and that he already lives quite far from them, I cannot see depriving your children of their maternal grandparents just because it's 5 hours closer to their their paternal grandparents (who are already at *least* a 5 hr plane ride away already)!
2) The excuse that the paternal grandparents are giving you (unless they are of limited mobility) about their being unwilling to visit you if you move seems very irrational to me. My parents would figure out *some* very creative way to see their grandkids even if it meant getting to Timbuktu on $100 or less! Where there's a will, there's a way. So why on earth would you stay in Ohio just in case his parents might visit? Again, unless they are not healthy enough to travel, distance and finances are not an excuse as they can be creatively dealt with.
3) Extended family is important, and you've got a lot of that in Oregon! I think that if you trust and get along with your parents, it is such a gift to have them living nearby for so many reasons, especially when you have kids! It also seems that you would be gaining access to even more extended family, thus possibly a stronger support network, by moving to Oregon.
4) Many, many people who move (those who do it frequently as well as those who do it only rarely) say to give a new city a minimum one year (12 whole months) before deciding if you want to stay or move away. Hopefully your husband would be willing to at least do a trial run in Oregon?
Anyway... best of luck to you in navigating the possibilities with your husband. Moving households *and* cities is one of the most stressful life events around, so it's likely this transition is making emotions and tensions run high for all of you, and it's good to have a lot of empathy for him, for yourself, and for your kids as you continue through this process. I hope you are all able to come together to find a win-win situation for your family regarding this move!