Is it permissible for a father to sell a house he owns in order to buy two apartments: one for his disabled daughter to live in, and the other to be rented out as a steady income for her, given that the rest of his children are financially stable?

The Sharia commanded justice between children and forbade favoring some over others in gifts, unless their circumstances differed and the condition of some necessitated favoritism due to need or illness, and not merely out of partiality. Therefore, there is no harm in favoring a disabled daughter and singling her out due to her illness, only to the extent of her need. Anything beyond that requires equal treatment between her and the rest of the children.