My friends and I created a Facebook group for programmers and alike. Its aim is to have members asking questions and others answering them.
If you want to keep your membership small on your Facebook page then asking them what interests them is the way forward, do they like the format of what you are doing, does it interest them. If their engagement with your group is so infrequent and each contribution so small perhaps you need to expand something, either the subject or the membership.
BTW, your page is not trivial to locate as there are quite a few 'Captain Luffys' (or Kapitan Luffy) on Facebook, and you're not on the list. Also your Twitter, named after the "Straw Hat Pirates", probably limits your membership to fans of the manga series "One Piece".
Members must enjoy a lot of the subculture totally unrelated to programming.
The Internet is huge, even Stack Exchange is tiny by comparison; politely I ask: What do you offer your members? Why visit your site and chat or ask when the answer they want is presented almost instantly in 1000's of other places. IF you were writing a game for One Piece you'd make a great resource (presumably), if not then there's only so many hours in a day.
Though members seem active, the active members I'm talking about are only 5 people out of 35 members.
That isn't "bad", but with so few members it makes for a peaceful place to visit.
What are the things that I should do to encourage (specifically the dormant ones) members more?
Be the place to go: a new great photo, an interesting question of the day, a headline about the latest episode and a chatroom for it. An interesting programming problem that you know will be popular (?? How to find loot ?? - I'm not familiar with the series).
There are realistic demands placed on people: family, work, school, chores, etc.
Without a membership of several hundred I don't think you can expect change without change. People's behavior and motivation isn't likely to change unless you can change your business model - more people steering the ship or more members to listen to the captain.