There is no distinction between primary and secondary owners of accounts for aggregation of cash transactions for CTRs.
Chris's deposit was made on behalf of each of the co-owners of account A -- Chris and Joe
Joe's deposit was made on behalf of each of the co-owners of account B -- Joe and Brian
A CTR is required because deposits totaling $11,000 were made on behalf of Joe. The CTR will list Chris as conductor for $6,000 on behalf of himself (2a) and Joe as conductor for $5,000 on behalf of himself (2a), plus Brian as a person on whose behalf $5,000 was conducted (2c). The total deposit(s) will be $11,000. Item 3 will be checked.