Sorry to hear of your loss.
If he made non deductible contributions reported on your joint return on Form 8606, you do inherit the remaining basis in his IRA. Add that basis to any basis you already have in your own IRA, and show the inherited amount on line 2 of your 8606. You do not have to complete an 8606 until you otherwise would need to, such as taking a distribution or RMD. Show the amount of inherited basis on line 2 of that 8606.
Note that while there may be non deductible contributions, there is no such thing as a non deductible IRA, even if all his ND contributions were made to the same IRA. Since those contributions were made there would be pre tax earnings generated in that IRA, and for tax purposes if he had more than one IRA account, they are treated as a single IRA. Form 8606 applies to all IRAs owned by each taxpayer.
If you need any assistance with RMDs including any RMD he did not take for the year of his death, please advise.