It sounds as if your fiancé could qualify as a dependent on
your tax return as a qualifying relative if:
- She
was a member of your household the entire year.
- The
relationship between you and the dependent does not violate the law (you
can’t still be married to someone else. Also check your individual
state law. Some states do not allow you to claim a boyfriend or girlfriend
as a dependent even if your relationship doesn’t violate the law).
- You
meet all the other criteria for “qualifying relatives” (gross income and
support).
Keep in mind that if the children are not your biological children, and if the mother of the children has an agreement with the biological father of the children regarding who can claim them on income tax returns, then that would be a factor in whether you would be eligible to claim them on your return. In order to determine if she and the children meet the IRS
definition of a "qualifying relative" please see the following TurboTax FAQ:
https://ttlc.intuit.com/replies/3288503
