Firstly you have to have bought the house for the guild and orphanage to accept your adoption i believe.
Twins: A day or two after you save them, go to where you sell items at the guild and talk to the woman. After you finissh selling your stuff, she'll comment on the twins you saved and ask if you want to adopt them.
Orphanage: 2 children can be adopted from the orphange, but itll cost a lot of money. Donate 100,000 to the orphanage and they'll ask you if you want to adopt a black-haired or brown-haired girl (i believe you get both so it shouldnt matter though i didnt test it). itll cost another 100,000 to formally adopt the girl you pick. After being granted the first adoption, repeat the process (another 100,000) and they'll let you adopt a second girl (so youll need 400,000 in total to adopt both).
Flower girl: At night, if ya go to the right of the house you buy and into the alley youll find a girl there who asks you to buy flowers. Each one cost 5000. Keep buying flowers from her and eventually the next time you meet her you'll just askif she wants to be adopted and she'll move in with you.
That should be all 5 (or at least the 5 i found).