My son in law forcefully dumped his son's responsibility to us

I am a 78 years old man and my wife is 71 years old. Our daughter has expired two years back and her husband got married again. Recently he has dumped his 14 years old son to our house with all his belongings and not taking his son since one month. It's not possible for us to tackle our grand son in this age as he is a hyper active child and is under medication since a long. Sometimes hebecimes very arrogant. Now kindly suggest if we can take any legal step to make his father bound to take his son's responsibility.