How do you stop a dog from biting family members?or other people?

ok so i got a miniature schnauzer had him since he was a puppy and hes never hurt a soul he was really good dog obidient nice and playful very very cute he is 3 yrs old now and a couple months ago he got this habit of barking aggresivley at people and barking and barking but he wouldnt bite as soon as they touched him he wud wag his tail and be playful but i had to bring my nephews to live with me and they wer playing they wud run around the house and he wud chase them i told them to stop and they wudnt just to agitate him so they eventually stopped but kept playing with him and days later me and my nephew wer on the couch watching tv and we wer play fightng over the remote and the dog jumped up and bit my nephew on his arm aggresivley i pulled him off and threw him outside and took care of my nephews wound why can i do to stop this he is very sweet and nice but he just gpt agrresive recently i dont wanna give him away or put him dow?