Earlier, he wasn't threatening and had just laid out facts, but now he was threatening. If they didn't agree or Riva continued her behavior, he was simply going to walk out of the room.
Sure it would be better for him and his companions if he could heal Sophie and others like her, but since he didn't have any Nascent Energy, nor any source to get some from, so if they didn't agree… there was nothing he could do about it.
Riva's expression changed and her pupils constricted into pinholes. She was still angry but finally seemed to have realized the gravity of the situation.
Whether he was trying to take advantage of them or not, if she wanted him to heal her daughter, she had no choice but to agree to his 'unscrupulous' demand.
Sophie looked at Max, who had closed his eyes, and then at her mother, whose face was one of anger and helplessness.