Working for a car leasing company as a frontend developer

My brother works for a car leasing company as a frontend developer, and he has been for 6-months now. Last week he realized something disturbing: there is a riba component to the cars that customers rent. It may be naive of us, but no one in our household was aware of this. Now, he does not actively work with riba related transactions (he doesn't make the contracts, doesn't witness it, and he doesn't do any calculations with riba), he just makes the user interface for the website and mobile app where customers can assemble their car etc. I am worried that his work there is haram because of the riba aspect of car leasing, even when his involvement would be more indirect. And if his work is haram, would it be okay for him to stay with the company while he actively applies to other lawful companies with the intention to leave when he gets the chance? He is still a junior frontend developer so his job options are a bit limited (companies here are mostly searching for medior or senior developers) so it might take him a while to find something else. Would it be okay for him to stay with his current company until he finds something else so he doesn't face a financial loss & he continues gaining more experience so it will also in sha Allah be easier for him to find another job? It is very important to him (and to me as well) that his work is pure and halal. His intentions are to work somewhere lawful so he is very worried and upset right now, so your advice would be greatly appreciated. Sincerely, A worried sister