You (or a lawyer) need to determine if the intent was to GIFT the house to the son, or if the title transfer was merely for other purposes, but the INTENT was the father would have full control of the home for all purposes (including receiving the sales proceeds if it was sold before his death).

If it was a Gift, the Basis was the father's basis (plus any Basis adjustments after that).
If it was a Life Estate, the Basis is the Fair Market Value at the date of death.

The fact that the son never used the home and the father used the home until his death definitely weighs towards the Life Estate.