Since you are not the custodial parent you cannot claim the child without the ex's permission and a signed form 8332. Support is not a determining factor any longer according to the IRS.
As to the boyfriend ... to claim a child that is not related to him he would be restricted to just claiming the child's exemption ( not any credit or HOH filing status) and only if the child lived with him all year and he provided more than 1/2 the child's support for the year. However if the mother has SSDI then the child does as well and the support test will be hard to pass.
If you want to turn them in for doing incorrect tax returns ... https://www.irs.gov/individuals/how-do-you-report-suspected-tax-fraud-activity
Or SSDI fraud ... http://www.disability-benefits-help.org/blog/social-security-disability-benefits-fraud
