I'm a bit confused about the position of all in these sentences:
We all will die one day
We will all die one day
Are they both acceptable? Is there any difference in meaning?
As a fiction writer I was taught that whichever comes first is the dominant word in the statement. It's like the difference between "red-blue" (purple) and "blue-red" (violet). If you wish to accent on "all," then the sentence is: "We all will die." If you wish to accent on "will," then the sentence is: "We will all die." Different English teachers might teach different 'schools of thought' on 'proper' word order, yet literary professors will tell you that fiction writers (contrary to journalists and nonfiction prosaists) have licence to use the language in favor of their creative goal, just as sculptors use clay without any art critic's restrictions. Therefore, there are NO grammatical, philosophical, or any other quarrels on the topic. It's all personal, in this case.
There is no difference in meaning. There is a slight difference in nuance, based on the word order. English has a rhythm to it, and certain words can feel more important or "accented" depending on where they appear in the sentence.
In this case the sentence, if set to poetry, would have an Iambic rhythm:
we ALL will DIE one DAY
we WILL all DIE one DAY
Here, the accented words are considered more important or significant in the sentence. Which you choose depends on whether you want to accentuate "all" or "will" -- either that all of us will die, or that every person will die.
Most native speakers recognize and respond to this kind of rhythmic variations even if they are not consciously aware of the rhythm, or have no idea what "iambic" is. However, this rhythm is fundamental to English poetry and music, especially genres like rap music, where the rhythm of the words is it own musical theme.
I'm sure you have something similar in your own native language. If you'd like to learn more about English rhythmic patterns: https://en.wikipedia.org/wiki/Metre_(poetry)