You have mentioned no rollover, only nondeductible traditional IRA contributions and Roth conversions. By "rollover" did you mean the carryforward of your $6,000 of basis from 2022 to 2023?
The $6,000 nondeductible traditional IRA contribution was reportable on your 2022 Form 8606 and is the only part of this reportable on your 2022 tax return. This Form 8606 should have $6,000 on lines 1, 3, and 14. If your 2022 Form 8606 did not show this contribution, you must amend your 2022 tax return.
The $6,500 nondeductible traditional IRA contribution is reportable on 2023 tax return. This will appear on line 1 of your 2023 Form 8606 to be added to $6,000 on line 2 (carried forward from line 14 of your 2022 Form 8606) producing $12,500 on lines 3.
The fact that your Roth conversion comprised two separate conversions is irrelevant because both conversions occurred in the same year. The two conversions are reported as a single Roth conversion by entering the 2023 Form 1099-R, indicating that you moved the money to another retirement account and indicating that you converted the entire $12,500 to Roth. $12,500 will appear on lines 8 and 16 and 17 of your 2023 Form 8606, resulting in $0 taxable on line 18.
