Do I have a right to receive a my security posit back from a new tenant if I’m signing an addendum?

Unless you are on the lease it is a really bad idea to have your money as the security deposit for other people. If damage happens, however it happens, the landlord will look to your security deposit to do the repairs and there is nothing you can do about it. Even if you have a writing from the other tenants promising reimbursement, you still have to collect from the others. Hard to do. Best for them to have their own lease and their own security deposit.