Filing returns individual and deceased husband joint or separate

Hello,

My dad expired last year. His final returns need to be filed with my mother being a representative. I have 2 queries

1, Can my mom file her own returns and then later on file returns of my dad (since succession certificate will take some time)

2 Also in relation to point 1 all my dad's bank accounts and FD's were all joint with mom as second holder,,in all those accounts my dad's name has been deleted so the money in all those accounts/FDs now belong to single holder my mom. Should all that money be considered as Exempt income.?

thanks