What you have explained is a parent/child relationship which is not what a multiple detail band is meant for. It's meant for parent + child1 + child2.

In your situation, create a relation between parent and child and use SET SKIP.

SELECT Parent
SET RELATION TO SomeID INTO Child
SET SKIP TO Child
REPORT FORM Whatever

On the report, create a data group on the parent ID field. Place the parent information in the Group Header band. Place the child information in the detail band. Do not fill in the "target alias" in the detail band.

As far as your question about printing the parent and child information side by side .. the answer is you can't define the report this way. If you want to do this, you will need to create a temporary cursor that has both the parent and child information in each record and then drive the report from the temporary cursor and place all information in the detail band.