filing taxes for deceased person

My dad died in 2021 & I'm trying to file his Federal & state tax forms. (he's owed a refund from Fed & owes money to his state). I have several questions:

1) regarding form 1310...it asks about a will. For purposes of form 1310, is a trust the same as a will?

2) for his Federal return, I believe I will need to mail his 1040-SR, 1099-R, & form 1310. Is that all the forms I will need to mail? 

3) Is it possible to mail in his Federal return (from which he's owed money) and e-file his state return? (he owes his state). I'm not able to figure out how to do that on TT. 

I would very much appreciate any help.