I have a family of 5 and my kids are 19, 14 and 10. My husband works full time and likes dogs but he doesn't walk the dog unless I ask etc. It's on me which is fine because the dogs make me happy. I'm the one trains, plays and feeds. THe kids walk by and play with the dog or pet and then 3 minutes later are off to something else. THey don't have time or an interest in learning the skills to manage the dogs much. I totally understand that you're mystified that a family of 5 can't entertain this puppy but the puppy honestly is sleeping way too much with your 18 year old in charge if they're lounging on the couch together. I understand this part.
I don't know where you live but if you're blessed with 7 acres to get this puppy out and active, please go buy each family member a pair of cheap boots from Walmart and tell them to bundle up get outdoors and get dirty with this puppy, I'd make it a requirement for the 18 year old especially. Every single day. THat's what it is going to take to live happily with this puppy for the next couple years. Take the puppy outdoors hungry and feed him kibble when he wanders off and you call him back to you. Have him learn to run back and for between two familiy members for treats.
If you have space in your home, purchase a few interactive things the kids can play with the puppy with https://www.amazon.com/100-Pit-Ball-...words=ball+pit
you can put those plastic balls into a big plastic baby pool or something like this and the puppy would love it. https://www.amazon.com/POCO-DIVO-Tun...ds=kids+tunnel
Get your husband to help you make something like this with a piece of board and a tennis ball: https://www.amazon.com/FitPAWS-20-Ca...ds=dog+agility
Things that the kids can do with the puppy and give him a treat or tug on a toy will be a reward for the puppy and keep him active.
A new trainer who specializes in agility games and competes with her own dogs might be a great help to you in coming up with things to keep this puppy busy.