Deceased Father who owes

My dad passed away April 2019 and didn't file his 2018 taxes.  He transferred money in 2018 from a 401k to an IRA.  Otherwise no other assets, no life insurance, no pension, no house, nothing.  He didn't transfer all of the money and kept out about $22,000.00 to live on.  He was diagnosed with cancer August 2018 and went on short term disability from work.  Anyways he owes now almost $6000.00 in taxes.  He had $2000. in his checking which helped pay for funeral expenses.  He is divorced and lived with my brother.  We are his next of kin, are we responsible for paying those taxes?