I've tested a similar idea for a milestone report I was working on, but the upkeep on the report ended up not being worth the effort comparted to using the built in grouping functionality.
Basically, this is looking for a particular milestone name to show info, you can replicate this with different milestone names to just show their relevant data. Might work for what you're looking for regarding the parent task.
Here's the textmode edits for the named milestone column "Charter Complete". I've bolded the rows that really force the "if milestone name = x" to generate the below info on planned complete, projected complete, and % complete. You should be able to modifty that from:
IF({milestone}.{name}="Charter Complete",CONCAT({percentComplete},"%"))
to something like:
IF({task}.{name}="Parent #1",CONCAT({percentComplete},"%"))
column.7.displayname=Charter Complete
column.7.sharecol=true
column.7.styledef.case.0.comparison.icon=false
column.7.styledef.case.0.comparison.leftmethod=condition
column.7.styledef.case.0.comparison.lefttext=condition
column.7.styledef.case.0.comparison.operator=in
column.7.styledef.case.0.comparison.operatortype=string
column.7.styledef.case.0.comparison.righttext=AR
column.7.styledef.case.0.comparison.trueproperty.0.name=bgcolor
column.7.styledef.case.0.comparison.trueproperty.0.value=feecc8
column.7.styledef.case.0.comparison.truetext=
column.7.styledef.case.1.comparison.icon=false
column.7.styledef.case.1.comparison.leftmethod=condition
column.7.styledef.case.1.comparison.lefttext=condition
column.7.styledef.case.1.comparison.operator=in
column.7.styledef.case.1.comparison.operatortype=string
column.7.styledef.case.1.comparison.righttext=IT
column.7.styledef.case.1.comparison.trueproperty.0.name=bgcolor
column.7.styledef.case.1.comparison.trueproperty.0.value=eac6c9
column.7.styledef.case.1.comparison.truetext=
column.7.styledef.case.2.comparison.icon=false
column.7.styledef.case.2.comparison.leftmethod=condition
column.7.styledef.case.2.comparison.lefttext=condition
column.7.styledef.case.2.comparison.operator=in
column.7.styledef.case.2.comparison.operatortype=string
column.7.styledef.case.2.comparison.righttext=ON
column.7.styledef.case.2.comparison.trueproperty.0.name=bgcolor
column.7.styledef.case.2.comparison.trueproperty.0.value=def6e2
column.7.styledef.case.2.comparison.truetext=
column.7.textmode=true
column.7.value=<b><strong>Task:  </strong>
column.7.valueformat=HTML
column.7.width=150
column.8.displayname=Task Name
column.8.listdelimiter=<div>
column.8.listmethod=nested(tasks).lists
column.8.sharecol=true
column.8.textmode=true
column.8.type=iterate
column.8.valueexpression=IF({milestone}.{name}="Charter Complete",{name})
column.8.valueformat=HTML
column.9.sharecol=true
column.9.textmode=true
column.9.value=</b><hr><strong>Planned Completion:  </strong>
column.9.valueformat=HTML
column.9.width=150
column.10.displayname=Charter Complete Date
column.10.listdelimiter=<div>
column.10.listmethod=nested(tasks).lists
column.10.sharecol=true
column.10.textmode=true
column.10.type=iterate
column.10.valueexpression=IF({milestone}.{name}="Charter Complete",{plannedCompletionDate})
column.10.valueformat=HTML
column.11.sharecol=true
column.11.textmode=true
column.11.value=<hr><strong>Projected Completion:  </strong>
column.11.valueformat=HTML
column.11.width=150
column.12.listdelimiter=<div>
column.12.listmethod=nested(tasks).lists
column.12.sharecol=true
column.12.textmode=true
column.12.type=iterate
column.12.valueexpression=IF({milestone}.{name}="Charter Complete",{projectedCompletionDate})
column.12.valueformat=HTML
column.13.sharecol=true
column.13.textmode=true
column.13.value=<hr><strong>% Complete:  </strong>
column.13.valueformat=HTML
column.13.width=150
column.14.displayname=Charter Complete %
column.14.listdelimiter=<div>
column.14.listmethod=nested(tasks).lists
column.14.textmode=true
column.14.type=iterate
column.14.valueexpression=IF({milestone}.{name}="Charter Complete",CONCAT({percentComplete},"%"))
column.14.valueformat=HTML