The individual volumes don’t matter your doses are always a fraction of 3ml (the total BAC in a pen), and the peptides are not in units, you‘re dividing milligram. If you want twice as much bpc than the other peptides, just put twice as much into the mix.
So if you have 5mg vials, you need 2 vials of bpc, 1 vial of cjc and 1 vial of Ipa. 4 vials total, add into 3ml water, and that dose is .5, .25, and .25mg so 1/20 of your 300 unit slin pen in other words, 15 clicks.
You didn’t say what mg value you of each, so your math might have to change, but the point is its al about adding them to the mix in the correct ratio.