Hi, this is my first post - i need some help with my astrophysics. I'm writing a sci-fi story where an Earth like planet has 2 moons. One of them is habitable and has conditions like Earth - like an atmosphere and so on (almost like a twin planet). The other moon would be smaller and more like our moon - uninhabitable and rock-like. I want the three to be as close together as possible. Some questions: Would such a system be possible? How large would a moon have to be to have a decent atmosphere and be habitable? Should i size the 'Earth' planet up from our scale to enable the moons to be larger? Are are there any factors such a system would bring up that i should be thinking about, in regards to the effects the 3 bodies have on each other?(gravity etc.) Any idea about how the moons would orbit, and how the large moon would effect the small? What kind of distance from the larger moon to the Earth planet is feasible? I really don't have a great mind for astrophysics unfortunately, but I'd like the scenario to be plausible if possible, thus i need a bit a help. Thanks in advance.