Rattling Noise in Interior

Rattles/ squeaks suck.
Seems you have isolated the area where these are occurring.
The typically cure is to use felt stripes, foam inserts or double sided tape, even clay.
The seat belt may be the trim panel area and vibration, so remove and inspect the trim then install deadeners where applicable.
The rear seat, may be the "leather" rubbing on adjacent areas, felt may be the answer here.
FWI since squeak, I would doubt that it is the seat latching or brackets (rattle), but don't rule that out.
Happy squeak hunting