Not my package help

Hi this is a weird question for glow lol but I’m young and newer to house living… my boyfriend and I live in a rent to own house that my aunt actually is renting us. The old renters moved out left no forwarding address over 2 years ago and we still get their mail and we got this package delivered 5/20. Like all their other their mail I was advised to put return to sender they no longer live here in the envelope so the post office will send it back. I did it for the box delivered 5/20 and sat it on our porch to be picked up. THE POST OFFICE HASN’T PICKED IT UP. It looks like grandparents mailed the granddaughter that lived here a package judging by names on the box and they paid $14 for shipping and I want to ensure they get it back I even have tried finding the old residents on Facebook to inform them of the box and other mail but had no luck. How do I get this box back to the original senders I feel so bad I’m probably going to tape money on the box because it sat so long and I don’t think they can get it back. My aunt advised to just write the same thing on the box and put it by our mailbox and it will get picked up and it hasn’t. I live in Michigan. Thank you in advance

Update: thank you everyone for the help I got lucky today and caught our mailman today and he gladly took it with him!!