i'm trying 2 convert a species into d&d format, but i'm having trouble with it

[Jakathi]

Dragonlord
(Fire-dragon, outsider/Celestial)
Ages ago, the hell-goddess Tiamat captured a descendant of Bahuma and forced him to have intercourse with her. She had planned on using the resulting children to foment confusion and dismay among the various good-aligned dragons.
Tiamat’s plans went wrong. Instead of having the form of a metallic dragon and the heart and soul of an evil, chromatic dragon, the exact opposite happened. Her children possessed her basic form and abilities, but had the general disposition of a good-aligned or neutral dragon.
The young dragonlords were quick to hide their natures and escaped hell at the first opportunity. When they reached the earth realms, they spread throughout the various dimensions, gleefully creating havoc among their mother’s forces.

They're basically immortal, with the ability to polymorph into any living form they desire.

can't quite seem to convert the critter.

 

[Salthorae]

ideas

Why not take a base Chromatic dragon, apply the celestial template, change the alignment to what you want, give them the Gold and Silver Dragon's Polymorph self ability or if you want to make it more powerful, give them shapechange as a spell-like ability. Keep the basic Chromatic abilities though so in look and in form they are the chromatic of that color, but with good alignment and celestial template (which to me implies immortality)...