Yes, you can contribute $7,000 for you and $7,000 your wife to a Roth IRA if you have enough taxable compensation (salary). The contribution to your TSP won't affect your Roth IRA contribution. You have until April 15th, 2020 to make the contribution for 2020.

Please be aware your Roth IRA contribution may be limited based on your filing status and income. Please see 2020 - Amount of Roth IRA Contributions You Can Make for 2020

Please follow these steps to enter the Roth contribution to track your contributions and verify you will not have any excess contribution because of income limits:

1. Open your return 
2. Click on "Search" on the top right and type “IRA contributions”
3. Click on “Jump to IRA contributions"
4. Select “Roth IRA”

Is it really a Roth IRA if you contributed via the TSP, and not a qualified after-tax Roth account in your TSP account?  Workplace Roth plans are NOT the same as IRAs and they have very different rules.  Generally, you would set up a Roth IRA at a bank or brokerage of your choosing on your own.  You can’t contribute to most workplace plans except via payroll deduction and you can’t make retroactive contributions.   (The limit is also much higher than $6000 or $7000 per year.)   You need to know exactly what kind of account you have.