You cannot claim your GF's children since they did not live with you the whole year----they spend some of their time with their other parent. Your GF can claim them if she is their custodial parent. You can claim your own bio-child as a dependent and file as Head of Household by claiming him as a dependent. You may receive child-related credits for that child only, such as the child tax credit or earned income credit or the stimulus payments (or recovery rebate credit).
If your GF has more than $4300 of income (not counting Social Security) you cannot claim her as a dependent.
Your GS's children cannot be your qualifying children, since they are not related to YOU. They cannot be your qualifying relatives, since they did not live with you the whole year. They lived part of the year with their other parent.
Here are the rules for claiming dependents:
WHO CAN I CLAIM AS A DEPENDENT?
You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2021 taxes as long as they meet the following requirements:
Qualifying child
- They're related to you.
- They aren't claimed as a dependent by someone else.
- They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
- They aren’t filing a joint return with their spouse.
- They're under the age of 19 (or 24 for full-time students).
- No age limit for permanently and totally disabled children.
- They lived with you for more than half the year (exceptions apply).
- They didn't provide more than half of their own support for the year.
Qualifying relative
- They don't have to be related to you (despite the name).
- They aren't claimed as a dependent by someone else.
- They're a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.
- They aren’t filing a joint return with their spouse.
- They lived with you the entire year (exceptions apply).
- They made less than $4,300 in 2021.
- You provided more than half of their financial support.
When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them. There may be other tax benefits you can get when you claim a dependent.
Related Information:
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
