Can I do my late fathers 2017 & 2018 taxes on turbotax? What do I need to do?

"What do I need to do?"

You need to purchase TurboTax products for 2017 and 2018 which, at this point, are only available for installation (i.e., no longer available for online preparation).

See https://turbotax.intuit.com/personal-taxes/past-years-products/

You would have to use the past years products for each year.

If an estate tax return (1041) is also required then that requires TurboTax Business which is separate from the personal versions.

https://turbotax.intuit.com/personal-taxes/past-years-products/

I suggest that you read IRS Pub 559 (Survivors, Executors, and Administrators) for a lot of good information about filing the final return and estate return and other requirements.

https://www.irs.gov/pub/irs-pdf/p559.pdf

Tax returns for past years cannot be e-filed. You will have to print the 2017 and 2018 tax returns, sign them, and file them by mail. See "Filing Reminders" in Pub. 559 for instructions for signing a decedent's tax return.