I love [name_f]Maggie[/name_f]! I also prefer the spelling [name_m]Marlow[/name_m].
[name_f][/name_f]If that is your feeling with [name_f]Maggie[/name_f] [name_f]Promise[/name_f], [name_f]Marlowe[/name_f] [name_f]Promise[/name_f] gives similar book title vibes [name_f][/name_f]- which is NOT a bad thing, but something I’m pointing out if you want to avoid that.
[name_f][/name_f][name_f]Maggie[/name_f] [name_f]Grace[/name_f] is adorable, as is [name_m]Marlow[/name_m] Grace…Promise is kind of out there but if it has special meaning to you, who cares?! It’s your baby! 
Congratulations!