If you own the home, then the rent should be reported on your tax return and then you can use expenses such as mortgage interest, property taxes and insurance for only the part of the home considered to be his portion. If you rent a home and you, the parents are the lessee and obligated for the rent. Again, you can determine his portion of the rental home. If he is being charged for his share of the utilities or paying his own portion of the utilities then this would not be entered on your return. His unit is determined by number of rooms or square feet whichever is the most accurate depiction of the area.
The effect on your tax return will be the same based on the terms above. You will still need to figure out whether he paid more than half of his own support. The worksheet link is very helpful. You basically put down all expenses for him (clothes, food, grooming, housing, utilities, capital assets such as a computer, cell phone, etc.) then subtract the income that came from his disability to see if your share his higher.
