life altering Update

My husband and I just learned about my 16 year old cousin needing a home. He is adopted by my grandparents. About 2 weeks ago my grandpa and him got into a physical altercation and he had my cousin taken away. No housing would take him so they locked him up in juvie. They said since no one can take him he won't get out until he's 18. My husband and I decided that we are going to bring him home in hopes of giving him a semblance of a life. I'm just kinda scared it will make a huge impact on my marriage. I'm also hoping that he can embrace a life with us. My question is how to help him get past his past of abuse? And also how to help him to adjust and feel comfortable in the new environment?