Opening Joint CDP account. Possible to link existing brokerage account?

Hi as above,

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I have an existing individual CDP account which is linked to DBS vickers and POEMS brokerage accounts. Is it possible to link the two brokerage accounts to the new joint CDP account which I am about to create?

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If yes, what happens when I buy securities through the brokerage? Is there any way to specify whether it would be deposited into my individual or joint account?

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Thanks!