.... usually 2 or 3 aren't being fed. We have tried holding them up to her and nursing but she is running out of milk and is getting very stressed when we do that.....
My approach in such a situation is to take the fattest third of the litter out for one feeding to give the others a better chance at the milk buffet. One good feeding can make a difference.
Personally, I don't try to hold the doe, mine are stressed by that and that, apart from the risk of injury, doesn't help. What a nursing doe needs is peace, food, food, and food. No stress. Imo, too much meddling can drone out their instincts, and stress costs energy.
You know that you can pretty much free feed the doe, about triple her amounts of pellets, you can also add about a Tbsp. kitchen oatmeal per day to give more energy.
Feeding formula, well, I tried a few times with no luck, it can easily upset the digestion. Others with positive experiences might be able to help there, but usually it's a last resort with high risks. Rabbit milk is something rather special.
There are a lot of very informative threads already here, use the search. Use the term "formula" and select "thread titles only"
Like:
https://rabbittalk.com/threads/updated-hand-feeding-formula.27372/