if my dependents (2 sons 21 years old, twins) are abroad, can I include them in tax filing?

[sanvik8888]

I transfer them money through third person

[xmasbaby0]

Are your sons full-time students?  If they are full-time students, living away at school is considered to be a temporary absence from home, so you can still say they lived with you and claim them as qualified children dependents.   If they are not students, then simply transferring money to them is not enough to claim them as dependents.

IRS interview to help determine who can be claimed:

https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent

WHO CAN I CLAIM AS A DEPENDENT?

You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2025 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 $5200 in 2025 (not counting Social Security)
• You provided more than half of their financial support

[Mike9241]

since they are over 19, to be classified as qualifying children for being dependents, they must be (these rules apply separately to each one) 

1) full-time students -  meaning enrolled full-time in school (but not online or correspondence schools) during any part of 5 calendar months during the year

2) their absence from your home must be temporary. 

3) they cannot provide over 1/2 of their own support 

Or regardless of age to be classified as a qualifying relative for being a dependent 

1) teavh must have gross income of less than $5200. The money you provide then is not income

2) you must provide ober 50% of their support. (applies separately to each one)