Supporting My Friend’s Path to Islam

Assalamu alaikum, I’m reaching out here for some direction and to find kind, approachable scholars who can advise me. A really close friend of mine grew up Catholic but now identifies as an atheist. He’s in a relationship with a Muslim woman, and they’re planning to get married. Her family and she have asked that he embrace Islam first, and he’s actually open to the idea-he’s been reading books and looking at online resources to understand more. But he’s been honest that if he says the shahada right now, it’d mainly be for the sake of the marriage. I’ve been asked to assist with the shahada, but before I take on that responsibility, I need some clarity. Is a conversion in this situation-when it’s tied to a marriage requirement-considered valid? I’d truly appreciate any insights or links to scholars I can talk to more deeply about this. And please, no judgmental comments. Jazakallah khair.