I assume that your step-father is still alive or there was no life-estate involved. You enter into TurboTax the $390,000 as the proceeds from the sale of investment property. Your cost basis and holding period are the giver's cost basis and holding period. The amount of taxable income to you is $390,000 minus this cost basis and is long-term if your step-father purchased the property more than a year ago, otherwise it's short-term.
Separately you have made a gift of cash to your sister. Nothing about this gift goes on your individual tax return. If the amount of this gift was more than the annual gift exclusion amount ($17,000 for 2023), you must report this gift on Form 709.
