If I am the legal guardian of my grandkids are they considered other or foster?

Are you supporting them?  

To claim a grandchild as your dependent

When you enter the child’s name in My Info, you will be asked “What’s your relationship to  [child’s name]?”  

           Choose “another person”

            a drop down menu will appear that lets you choose grandchild

WHO CAN I CLAIM AS A DEPENDENT?

You can claim a child, relative, friend, or fiancé (etc.) as a dependent on your 2024 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.

A grandchild has the same status as a son or daughter.  Use that.