As you would expect, modules that are nested hierarchically must also have a nested floorplan. A child RP must have a pblock that is completely contained within its parent RP pblock, for all resource types. Expanded routing regions are supported and on by default, but they are created slightly differently in Nested DFX - routing expansion for lower-order RPs will fill the parent pblock, but will still never overlap another RP at the same level. Use the hd_visual scripts to see the placement and routing regions for any RP in the design.
Partition pins are automatically managed by the Vivado tools and are established no differently for lower level RPs. Location ranges and constraints can be used if desired. Partition pins may be eliminated if the source and all loads are within the expanded routing region of the target RP.