I would contact an ADA specialist to help you with your design. He may have special needs that need to be considered when creating his side of the living quarters

Also check with your zoning office if you plan to add a separate kitchen to that space, I turned a few houses from single family to a Mother Daughter setting and they had to go in front of the Board of Adjustments. In most cases they will allow it, the only thing you will have to sign an agreement that it will never be used as a two family house and you will not be renting out the space.

Best of luck