Should the wife inform her husband about the problems caused by his teenage brother living with them, and what is the ruling on him hearing her voice and seeing her?

There is no harm in speaking with your husband's brother if circumstances necessitate him living with you, provided that you do not speak in a soft or alluring manner, as Allah Almighty says: "Then do not be soft in speech, lest he in whose heart is disease should covet, but speak with appropriate words." The conversation should be limited to what is necessary. Care must be taken not to expose any 'awrah. If you notice him intentionally looking at you, advise someone who can advise him. If he does not respond, inform your husband to find a solution.