Their is an immortal coin, however it doesn't instantly make the immortals mortal. They are reborn as a mortal child infant. They sent the rest of their new born life unaware what they used to be.
After using the coin it goes into hiding. If its found the person can become immortal again if their other side is released. You know if it was used because it changes color.
Usually if you use it on 1-4 immortals the coin with never let them have the immortal side back unless they had it in their hands and will it. However, say you use it on 1 or 2 phoenixes, the coin doesn't need to be in their person or anywhere near them to regard immortality they just need to will it or die.
When normal immortals turn mortal die they don't puff back to their immortality. Since phoenixes are unable to permanently die, when their now mortal self dies they go back to normal They remember everything they held dear/important knowledge learned before becoming mortal this, doesn't always mean they'll have the same mindset or personality as before
The immortal coin was made to give the phoenixes a break.
When phoenixes "permanently die" they have are remade into new people with only the some knowledge of all immortals.
When they have kids which everyone took the phoenix gene completely will absorb the parent (If it's the mother they wait till they're no longer breastfed)
I say full gene because a person can have part of the gene were they can't be killed but dies of old age. Their are more combos but you get the gist.
The number of phoenixes say the same, 5 in total. If two phoenixes get together they will always have twins and they would always get the full gene.
If it's one phoenix its 50/50 on if the parent stays.
