I'm still working on Aura of Life. This works for the first part
Code:
Aura of Life; AURA: 30 all; Aura of Life; IF: FACTION(!foe); RESIST: necrotic; IF: DYING; REGEN: 1;
I still can't seem to figure out the hit point maximum can't be reduced part. I don't know if it is possible without the ability track the current HP max before and after an effect would attempt to reduce the HP max like the Wraith's Life Drain attack.
"The target must succeed on a DC 14 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken."