I’m so sorry for your loss 
I like the sound of [name_m]Owen[/name_m] [name_m]Forrest[/name_m] [name_m]Levi[/name_m] [name_f][/name_f] [name_f][/name_f]- it keeps elements of [name_m]Finley[/name_m] while clearly honoring your brother [name_f][/name_f]- however, reading some of the other comments, I think [name_m]Owen[/name_m] [name_m]Forrest[/name_m] [name_m]Blake[/name_m] is a good way to go. It flows nicely, but as you mentioned, you don’t want his name to feel heavy or sad to you.