I would include two part 1 sections for your customer: the first with item 2a and 3 checked, for the cashier's check purchase; the second with items 2b and 3 for the $13,000 cash toward the transfer to the family member's account.
Then, of course, there would also be a part 1 section for the family member with item 2c checked, again for $13,000.
Clearly, there is no guidance from FinCEN directly on transactions like those you have described. But I think a CTR completed this way covers the intent of the CTR filing requirement.
Don't forget that you also have two other records to complete and retain. The first is for the cash purchase of the cashier's check under 31 CFR 1010.415(a)(1) and the second is for the funds transfer of over $3,000 under 31 CFR 1020.410(a)(1).