Niko, Light of Hope and making his shards copies of Soulherder

Say I have [[Niko, Light of Hope]] and four shards on the board, alongside [[Soulherder]]

Niko reads "...shards you control become a copy of it until the beginning of the next end step"

Soulherder reads "At the beginning of your end step, you may exile another target creature you control, then return that card to the battlefield under its owner's control."

My question is this: I exile the soulherder with Niko before end step, sometime during one of my main phases. It becomes my endstep, and now I have four soulherder copies on the board. Would it trigger in such a way that I would eight shards, two for each soulherder choosing to flicker Niko, or would they all enter/resolve at the same time and only give two shards due to not being able to target Niko, assuming that that would happen at all?

Since they both say "At the beginning of the next end step" I'm uncertain of the ruling