Do I need to enter k1 income if it looks like the income was already included in the 1099 download from my brokerage (vanguard) account?

It is not uncommon to have investment sales reported on a Form 1099-B and have that same information also reported on a schedule K-1. You can just enter it in one place or you can adjust the cost basis to equal the sales proceeds on the Form 1099B entry and then report the loss or gain on the K-1 schedule entry. The later choice may attract less attention from the IRS, as they may attempt to match up the K-1 and Form 1099-B entries to what you report on your tax return. If one of the entries is missing they may assess additional tax or send you a letter of inquiry.

You will see an option to adjust the cost basis of your investment sale reported on your Form 1099-B when you enter the sales information in TurboTax: