Give the threads you start useful titles.
Limit the number of questions in each thread. Ideally to one question.
Americans use "the" with "hospital." He's in the hospital. She is at the hospital visiting him.
Yes.He is in school. (Enrolled as a student)
Yes, or "he is at the school."He is at school.(For some different reasons)
No. "He is at church" means to me that he is attending a service at the church at the moment.He is in church.(To pray)
He is at church.(For some different reasons)
"He is in the church" would mean he was in the building. As would "he is at the church," though with "at" he could be outside or inside the building.