Hello
For the first scenario, you can simply use planning strategy 40 (see SAP Help for details).
The second scenario is more complicated. You can use for example, planning strategy 11, where system will consider only the PIRs to plan, but then sales orders are not considered as requirements. As a workaround, you can try to use BAdI MD_CHANGE_MRP_DATA to make sales orders relevant to MRP.
BR
Caetano
