Social security payments would not be taxable to you in the US. Based on the US-Germany tax treaty, you report US social security on your tax return in Germany just like German social security.
If you had taxes withheld in the US on that income, you would need to file a nonresident alien (separate for each of you) return on form 1040NR, which is not supported by Turbotax.
Have you talked to the German Rentenversicherung about consolidating the German and US social security accounts?
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