Making new Gas Giants might seam like a unfamilar idea.Usually it would be like creating a new Earth that is about 10,000 km across but it is not. Gas giants make great systems of their own.Jupiter has 4 giant moons.Saturn has 1 Giant moon and 7 other medium size moons.It is likely that gas giants are as easy to make as any terrestal.This process do not have to take a billion years to make.This process can be done in thousands of years.
We can mine minerals from Alpha Centauri A before it turns into a metal poor star.Important elemants can be taken out of the star and used as process for the moons.The non important metals can be used to form the gas giants. We will need fuel from the star to form planets as large as Jupiter. Alpha Centauri Ab and Ac will now need moons to live on.The moons will have to come short after the planet turns into a super earth.The moons will make terraform from a diffrent solar system easier The moons will also have to orbit far to give room for the future Gas Giant. People living on Alpha Centauri Ab.1 will be making the thick atmosphere around Alpha Centauri Ab.They will also need to make and atmosphere around their moon and others.The moons will also have to be at least Mars size to have and easy terraforming.
Alpha Centauri Ac will also be orbiting inside the habitable zone of its star. Alpha Centauri Ac is far enough to make rings around the planet.The habitable zone is bigger for this star than the sun is because it is a F type star and our sun is a g type. Making rings could include coliding two large objects and cause the planet to have a ring system.
If we were to make more Jupiter size planet it will have to be outside of the habitable zone. Alpha Centauri Ad Will be between the orbit of Mars and Jupiters orbit in that star system. Others will follow the same path as the first 3 planets in that star system. Moons around gas giants could create more room for earth like civilzations