I love the name [name_f]Autumn[/name_f]! I think it’s so pretty sounding and love autumnal vibes in general. Knowing that it’s an honor name for your grandfather makes it even more special!!
For nicknames maybe [name_m]Autie[/name_m], [name_f]Attie[/name_f], [name_f]Annie[/name_f], or [name_f]Amy[/name_f]?