British English accent is necessary (you don't need to be British for this role, you just need to use the accent).

Voice of a boy in his late teens (17-18), yet slightly more feminine.

Theo presents himself as this innocent kind boy, but his more aggressive, cold, true self shows in presence of his stepfather.

First line: tone- Theo is playing along, his tone should be polite and innocent.

Second line: tone- from confused and nervous to angry and finally sad.

Third Line: tone- full of anger, resentment and bitterness.