What a predicament! Any chance you could let them free range a bit each day so they caould forage for themselves? I have no idea what Alaska is like in the summer. My broody has three chicks that are coming up on 5 weeks and they have been free ranging since about a week old. They eat very little of their crumbles and mainly eat grasses, any seeds they can forage, a little scratch and bugs.
If it were me, and you can't free-range, I would offer a wide variety of feed and put that on the side/in addition to the stuff you have to extend it. I would stick to bird food and not go for the horse pellets unless I really had to. I would use hen scratch if its available cracked corn or soy if not, with the oats added in, get a mixed birdseed, and get some meal worms if they are available, They sell them for hens as well as reptiles.
I also do feed scaps and leftovers of what I eat to my girls. That is one of their jobs at my house. Cooked rice and other starches like cooked noodles and potatoes, scrambled eggs, various veggies and fruits , cooked meat (I avoid chickens cuz it just seems wrong) and dairy like yogurt and cottage cheese. I try to give a mixture and aim for a protein of about 20-25% to keep it balanced. Mix it all up in a pie plate and call them over. They get very excited and snarf it down.
They will survive and be fine, try not to stress about it too much!