The IRS will have this portal updated later this year for dependent information to get the 2021 advance Child Tax Credit - https://www.irs.gov/credits-deductions/child-tax-credit-update-portal

Hi Jasmine!

Parents of twins can receive up to $7,200.  If you'd like to receive monthly payments this year, the IRS has set up two online portals. The Child Tax Credit Update Portal will allow you to report any change in status (dependents, income) throughout the year. You will be able to use the portal to make sure your information is correct, including adding your twins.

Here is the link for you to enroll to receive payments. Click here.

Here is also FAQ page