It is kool that you and your wife are taking that big step. There will be trying times for both of you in the comming months and years. Just remember to talk to your wife about everything. Also if there are any support groups that you can get involved with in your area that would help. I hope that you two aren't the only ones to take care of him. Meaning that hopefully there are other siblings that can help out from time to time so that you two can get a break.
Good luck.