Okay, I like your concept, in fact I have been waiting for this kind of story. I want to think of what is happening with Thel. However, you have a few mistakes (nothing big).

1. The Sangheili dropped the "-ee" at the end of their names after the Great Schism. The "-ee" denotes service to the Prophets.

2. The Sangheili never acknowledge blood lines. The sons don't know their fathers, and the fathers are not allowed to see them. The sons are adopted to be raised by other clan members.

3. Please insert a line break after each dialogue. Example below:

Herp said, "Blargh, honk dshhife."

Derp replied, "Sfhidfh herpina."

4. quote: "I ducked UNDER a Banshee"? Please change it to "I ducked as a Banshee swooped low... etc"

5. [You can ignore this if you want] The Sangheili and Jiralhanae hate each others' guts. They never fight together unless ordered by the Prophets. Since they are now dead, the Brutes shouldn't be here.

6. quote: "The pelican retreated to the safety of the..." The what? Please complete.

You have a good knowledge of Halo lore, although there are tiny parts missing. Your writing style is decent and I sense potential. Edit as I pointed out and the story will look much more polished. :)