From what I recall, dicknipples should function like normal nipples, able to express the milk fluid type via milk ducts; yet they also have an added ability to ejaculate the cum fluid type if written to mention such (I assume the same with cunt nipples, but with the girl-cum fluid type). Usually authors write leaky nipples with the milk type, and rarely ever acknowledge different nipple types.
Usually, any fluid expressed will refer to its own quantity, so milk will be the lactation quantity, cum will be cum quantity, and girl-cum will be the girl-cum quantity. If it is written generically/unspecifically independent, that is fine too, but if you are looking for exact number ranges, they should probably correspond. I assume it to be this way since genital tails normally follow this method.