Could you please ask a complete question so we can understand what you are trying to do?

filing head of household and When I add my disabled mom and 78 years old grandmother dependents, TT states yes they qualify and the refund amount goes up. the moment I enter their social security number,  the refund amount drops back down. Why is this happening?

When you started to enter the dependents the "stimulus" for a dependent might have started to kick in.  But you cannot get stimulus money for claiming adult dependents.   So when you entered more information the "refund" disappeared.

All you get for claiming those adults is a $500 credit for other other dependents for each one--which can reduce the tax you owe.  It is not added to your refund.   And they do not receive stimulus checks since they are claimed as dependents---so be very sure you can really claim them.

CREDIT FOR OTHER DEPENDENTS

https://ttlc.intuit.com/questions/4499708-what-is-the-500-credit-for-other-dependents-family-tax-cre...

https://ttlc.intuit.com/community/children-dependents/help/what-does-financially-support-another-per...