Dude, 4:00 is after 12:00 so it is afternoon!
If you are gioing to be a guest then be dress casual dressy as it is going to be HOT in Aug.
I am going to a Stand up funeral myself today for My Best friends Daughter who is like a Neice to me.
Blazer and Slacks.
Dont go and be miserable. Maybe check with some of Your Brothers and see what they are wearing.