Yes, it is possible and you are a good sister in law for caring enough to ask. I invite you to go one step further, go to Barnes and Noble and invest in the following books.
1.- Self Help Skills for people with Autism spectrum disorders by Stephen R. Anderson
2.- Potty training strategies for people in the spectrum ( I can't remember the author)
There are a lot of books out there that can help people in the spectrum improve. The main thing is to view autism as something that can be work at and with visuals you can get points across to almost anybody. The best advice I can give you is to focus on communication, communication is everything. Speech Therapy is a must, your niece/nephew can also benefit from Occupational Therapy.
It is great that your BIL has somebody willing to help. Kudos to you. There are some good groups here for children with special needs, maybe you would like to check them up.
at 10:18 AM on Dec. 18, 2009