In a Resource Pool hierarchy, changes made to resources available to a Parent Pool affect:

In a Resource Pool hierarchy, changes made to resources available to a Parent Pool affect:

A.
Child Pools

B.
Sibling and Child Pools

C.
Sibling Pools

D.
Root Resource Pools

Explanation:
Page 45 from vsphere-esxi-vcenter-server-50-resource-management-guide.pdf

A resource pool can contain child resource pools, virtual machines, or both. You can create a hierarchy of shared resources. The resource pools at a higher level are called parent resource pools. Resource pools and virtual machines that are at the same level are called siblings. The cluster itself represents the root resource pool. If you do not create child resource pools, only the root resource pools exist.
Because the resource pools all get their available resources from the level above.
If, for example, you increase or decrease the memory reservation for RP-QA then this will affect the resources available to RP-Marketing because there will be less overall resources available.