You can split a pension with a deceased taxpayer in the year of death, but you must file the tax returns separately. 

Turbo tax and other software programs will not allow the returns to be prepared together because one spouse's marital status will be 'married' (At time of death) and the other spouse will be widowed (Dec 31) 

You will need to start new tax returns for both, TurboTax will ask in the beginning if "one of these returns is for a deceased person", and you must answer Yes, then answer the questions accordingly.