Ask Eat.Drink.Lagos XI
NOSA: RSVP sounds like exactly what you're looking for. The ambience is fantastic and if Instagram has told me no lies, the pictures there always bang.
FOLLY: Nosa is right about RSVP and pictures - it always clicks. Ginger Tapas is also an option, sharing plates would be cute for a girls hang out. La Verandah also has lots of natural light and great food, you pictures will definitely go platinum on Insta.
NOSA: If this birthday is on Wednesday/Sunday, you have to jump at pizza & wine at La Taverna. If it isn't, I'd say Petit Paris but I doubt they fit take 15 people in that place. You should give Basilico a shot. It won't blow a hole in your wallet, but the food can be hit or miss if you stray outside the pastas.
FOLLY: People seem to love Crust & Cream for things like this aka birthday dinners. It's not my favourite place, but others love it way more than we do, and so you may too.