Is there a presence in my house?

In Oct 2010 my husbands terminally ill uncle came to live with us. He was an odd character, spoke to himself... carried conversations with people we couldn't see (overheard him arguing, talking etc.) and we didn't really give much into it but my children started seeing shadows, hearing footsteps, and sometimes hearing things. After developing a pneumonia, he was hospitalized and passed away in April. Since then my children don't feel at ease, and I have a very difficult time sleeping. I'm not afraid by any means, but sometimes feel as if I'm being watched while in bed (only). My children always saw/heard things in the hallway which leads into my room... ironically, I do too. What is happening and why did it start even before he died? Mind you that he did not die in our home.