I did simplify the board-state to the detriment of the Felisa triggers.
So; I know Reyhan can see itself die, thereby moving its tokens to another creature, correct? Felisa would also see itself die in the same capacity, correct?
So say Reyhan and Felisa are both targets of the Devour, the counters on both could get moved by the Reyhan triggers to the new Thrinax, a number of Inklings equal to the counters from Reyhan and Felisa would enter, and then a number of counters equal to the number of counters on Thrinax would then be put on each of the Inklings that entered, correct?
Devour doesn't target, rather you choose which creatures to sacrifice as the devour creature enters. This means, that your choice of sacrifices cannot be responded to.
You get one trigger from Reyhan and one or two triggers from Felisa (if Felisa also had counters on it), meaning there will be potentially two instances of Inklings entering the battlefield. The Thrinax is on the battlefield at that time, so is a legal target for Reyhan's trigger. If you order the triggers correctly, those counters will be on the Thrinax when the first batch of Inklings enters. Then the second. Each Inkling will enter with a number of counters equal to what's on the Thinax at that time. This is a replacement effect, so happens immediately with the tokens being created.