Credit Karma and TurboTax are separate products and require separate accounts. You can't use your TurboTax info to sign in to Credit Karma and vice versa, though you can link your accounts together. See this help article for more information.
You also can't share a TurboTax Online account with another person to file returns. Each separate TurboTax Online account will prepare one Federal return for the year and can add multiple state returns.
You will either need to have your own separate user id and password to prepare your return using TurboTax Online, or you can choose to use a Desktop product, which can prepare up to 5 returns.
See this TurboTax help article if you had a separate TurboTax user ID and password but forgot either of them.