Well we dont know if Astlan Gods are immortal.
Definition of immortal being someone who is not able to die, no matter what.
I think the Astlan Gods are only as immortal as the Demons are, i.e. really hard to kill. Well mostly harder to kill than Demons.
We also dont know if an child of an god has the power of an god.
If its more like the Demon affspring: power of father + power of mother divided by two…