My sons wife wants to claim him on her taxes but she has only worked about 3 months he is disabled and they live with me who should claim him

[Carl]

If your son's status was married on Dec 31 of the tax year, nobody can claim him as a dependent. His choices are to file MFJ with his wife, or the two of them can elect to file MFS.  Note that MFS is the MOST EXPENSIVE way for a married couple to file their tax return.