I am glad you have your dad and your brother around, you'll all be a great comfort to each other.
Grief is lonely and isolating but having someone who truly "gets it" does help.
I am sure your mum wouldn't have known, there would have been signs as you say.
Everyone feels differently about seeing their parents body. I saw my mum after (only as she was left where they worked on her, in the middle of the living room). One of my brothers had to sit in another room though. I decided against seeing her beyond that point though - whereas my dad and sister did see her.
Personal choice and there is no right or wrong.
I hope knowing we've all been there and are still there, can help in some way. You are alone but not alone x