I'm in a hurry so pardon the bluntless. First, vet check. Like Grabby said, sudden behavior changes need to have medical causes ruled out, including hormone imbalances. If finances are an issue, apply for CareCredit.
Second, go back to housetraining 101. We have a subforum for that and the first post on the list should be our how-to sticky.
Third, yes, he needs puzzle toys, stuffed Kongs, and chews--rotated--to give him something to do. Find five minutes in the morning, afternoon, and night-time to fit in some play (flirt pole, tug, fetch, chase, hide/seek, walks, something) and training.
Fourth, Training should be positive reinforcement and doesn't have to be always have to be for the important stuff--tricks are fun, challenging, and endless options. We have a whole sticky subforum on training, including the Helpful Videos thread that could get your started. Five minutes a couple times a day will make a difference.
Fifth, Management--if you don't want to crate him, get an ex-pen for re-house-training. Perhaps designate one room that is off limits to the dog and make it the son's play room, toys stay in it; or designate one common family room for the dog and keep son's toys picked up. Use baby/pet gates to keep the dog in his safe zone. The chewing and eating of things is 100% management and owner responsibility. Keep them out of reach and give him something to do instead.
Sixth, sticking him outside is teaching him nothing, is denying him social time with his family, and is likely doing nothing/little to stimulate his mind/body. If your goal is exercise, he needs engagement with someone. Again, focus on short sessions of five minutes. This could be while you've got something simmering on the stove, on commercials if you are relaxing at the end of the day, etc.
Unless your family is unwilling to put in a little work, I'm failing to see the need for rehoming him. Your lifestyle sounds very typical of American working families, to be honest. While he doesn't seem to have major behavioral problems, untrained adult dogs are not exactly on people's wish lists, and you have seven more years of caring for him as incentive to work on this than any other person out there. If you don't want him anymore, you're going to have to put in the time/effort to find him an appropriate home with the patience and ability to deal with him, so you might as well start addressing everything now.