No, you cannot file multiple years together. You have to file a separate tax return for each year.
You can't use TurboTax Online to file for past years. TurboTax Online is only for the current tax year, which is now 2020. To file for earlier years you have to use the CD or download TurboTax software for each year that you need. You can purchase downloads at the following link. There is no free filing for past years.
Past Years' Products
You might get a better price from a reputable online seller that still has TurboTax in stock for the years that you need.
Tax returns for past years cannot be e-filed. You will have to print your past-year tax returns, sign them, and file them by mail. Mail each year in a separate envelope.
