Draw both buildings. Mark the school as: building=yes building=yes; amenity=school amenity=school; religion=christian religion=christian; denomination=baptist denomination=baptist; operator="Southern Baptist Church". Then add the address etc. For the church, it will be the same, only amenity will be place_of_worship. If you want to group them together in a relationship then select both buildings, then press Ctrl + B to create a new relation (JOSM). Edit the relation and provide the common attributes there and individually tag the individual attributes.

Draw both buildings. Mark the school as: building=yes amenity=school religion=christian denomination=baptist operator="Southern Baptist Church". Then add the address etc. For the church, it will be the same, only amenity will be place_of_worship. If you want to group them together in a relationship then select both buildings, then press Ctrl + B to create a new relation (JOSM). Edit the relation and provide the common attributes there and individually tag the individual attributes.