I'm not sure how that could work. All the receivers are connected to the SWiM switch. If you place a filter between the SWiM switch and the DVR to prevent sharing, then how would receivers within the same apartment be able to share with each other to do MRV? That doesn't make sense.
Right now, you have every receiver going to a 1x8 splitter. To isolate each apartment, you will have to add a 1x2 splitter downstream and have the receivers connect to that instead. From there, you can see where you add the Band stop Filter:
DIRECTV Band Stop Filter (BSFR01) - DIRECTV - BSFR01 -
As far as the internet goes, this should also be isolated by the BSF, but if it isn't, you should be able to limit internet traffic to those devices in your apartment.
That being said, it makes no sense that the installer left you with fewer working receivers than before he came to your property and then expects you to pay $50 to fix it. Are you dealing with Directv itself or a local subcontractor?
To me, it seems like you have an accounting problem that only Directv can fix, in addition to your technical problem. You can try sending an email to Ellen Filipak, VP of Customer Service to see if you can get this resolved:
eafilipiak@directv.com