The Issue is not your Hoppers, it is that you use Item Pipes in such a critical Setup.
What you should have done is use a single “Queue Hopper” prefilled with all Ingredients you need.
Or that you should test your Redstone before actually wasting things, you know you could just place a Chest where the Crucible is and see if it works before wasting Materials, right?
If you set 3 Hoppers to emit an exact amount and pulse them once with Redstone, they should give you the proper ratios too. Then you obviously need to wait until the path to the Crucible is empty before you pulse it again, or use a Queue Hopper after those 3 normal Hoppers to make sure the Order is kept.
Just do NOT use Item Pipes for this, its not going to be stable if you do that.
Edit: Also maybe dont flood your Crucible so hard if you want to make Steel, the Air from the “Bellows”/Engine needs actual space to fit in there too.