I agree with giving him time.
I would have inside toys, that he doesn't have all the time, just when you are there. And I would have have a variety: a squeaky toy, a ball, a couple different types of stuffed toys, maybe a kong that you can put treats in, and something to chew on, and possibly something to tug with.
Sometimes we have to make the toy make noise or play with it a little to get them interested. A plastic bottle will crackle when you crunch it for the dog.
For now though take some time each day to calmly groom his coat, handle his feet and his ears, and take him for a walk. Praise him for pottying appropriately, and offer treats several times during the day. Talk to him while you are cooking, (and slip him something), and while you are doing other things. Just explain what you are doing and why.
Give him the opportunity to come to you for pets. And other than your daily grooming, and taking a walk, let him relax and decide to come and see what you are doing. If he follows you into the room, talk to him, while you are doing whatever you are doing.
It might take a while to get used to the rhythm of your home and his new people. And sometimes dogs learn from other dogs. Like if you have the toys there, and he isn't interested, and at some point a friend comes over with a dog and their dog starts playing with your dog's toys, suddenly they have a higher value. Sometimes.
Heidi Ho, Odie
Joy-Joy, Bear Cub, Hepsi-Pepsi
Cujo2, Karma Chameleon
Ramona the Pest, Kojak -- who loves you baby?
Tiny Tinnie, Susie's Uzzi, Kaiah -- The Baby Monster.