Does True Son reconcile his Indian and white identities in The Light in the Forest?

Initially, there is no conflict within True Son. He loathes the idea of going to live with the whites and can only think of the time when he will escape and return to his father Cuyloga and his Lenni Lenape people. He dislikes everything about the whites until he meets his real brother Gordie. The young boy helps True Son to change some of his attitudes toward the whites. When he and Half Arrow kill Uncle Wilse and escape Paxton Township, True Son is glad to be leaving behind the white world with its "plaster walls" and confining clothes. He does, however, feel remorse and an inner conflict about leaving Gordie behind:

His only shaft of regret was leaving Gordie. He could see him in his mind now, lying alone on their wide bed, a chattering squirrel by day, a bed-warming stone by night, only a little minny of a fellow waiting for his Indian brother to return.

This conflict continues when True Son learns in Chapter Fourteen that some of the Indians of the raiding party have taken the scalp of a small child. He had earlier bragged to his white mother that it was only the whites who committed such atrocities. He cannot reconcile what he feels is a breach in the etiquette of his Indian brothers:

But all the time the tender pieces of discarded scalp with long soft hairs the color of willow shoots in the spring kept entering True Son's blood like long worms clotting the free wild flow. He tried to forget what he had said to his white mother, that never had he seen a child's scalp taken by his Indian people.

True Son cannot accept the idea that the Indians, whom he always thought to be noble and above such barbarism, were no better than the whites. This internal conflict finally prompts True Son to act in a way that reveals his feelings for the whites when he signals to the men on the flat boat that they are about to be ambushed. He sees a child about Gordie's age on the boat and cannot go through with the ruse to get the whites to come close enough to shore for an attack. This behavior is ultimately seen as traitorous by the Indians and True Son is eventually abandoned by them and expected to live the rest of his life with the whites. The internal conflict is never resolved. True Son will probably never be happy in the white world and he realizes this in the book's final passage:

Ahead of him ran the rutted road of the whites. It led, he knew, to where men of their own volition constrained themselves with heavy clothing like harness, where men chose to be slaves to their own or another's property and followed empty and desolate lives far from the wild beloved freedom of the Indian.

It is ironic that the honor and morality which is ingrained in him by his Indian father Cuyloga is exactly the reason why he is no longer able to live with the Lenni Lenape. He had learned his Indian lessons too well and could not abide the hypocrisy which was exemplified by the taking of the child's scalp, regardless of motive. 

How did True Son acquire his Indian heritage in The Light in the Forest?

True Son’s Indian blood is metaphorical.  His adoptive father conducted a ceremony to replace his White blood with Indian blood, to make him the “true son.”

True Son was captured from his White family by the Delaware Indian tribe when he was very young.  As a result, he thinks of himself as an Indian.  Apparently, his new family wanted to make it official.

More than once he had been told how, when he was four years old, his father had said words that took out his white blood and put Indian blood in its place. (ch 1, p. 4)

According to his father, his “white thoughts and meanness had been wiped away” in this ceremony, and an Indian’s brave thoughts replaced them.

Not only is this an example of how invested True Blood’s adoptive parents were in him, it is also an example of the indoctrination he underwent.  True Blood was taught from the age of four that he was now an Indian, and he was strong while his former people were weak.  This makes returning to them all the more difficult for True Blood.

True Blood is remembering this ceremony at a time when his father is returning him to his white family.  He does not understand how he can be treated as a son for so long and then cast away, returned to a family he no longer knows.