Gonna give some of my own opinions on this. Well people seemed to answer your questions on “what” but kind of ignored the “how” and the “why” so I shall tackle that.
a: As the other members said, it is just the 10 of them. Not sure about the girls in the EX routes but I haven’t read nor watched those yet. Now, you do have a point, they didn’t really meet with their family and settle things. But the thing is they didn’t really need to. All of the problems they had were problems of their own which, subconsciously, they knew how to solve, but couldn’t muster the strength to do so. And that is how Riki helped them. So even if Kanata is actually a bitch in the real world and doesn’t care about Haruka, the problem that Haruka solved was the problem with her own perception. And I guess all the stuff that Komari’s grandpa knew are things that Komari knew, perhaps subsconsciously (see next item)
b; I’m honestly not sure, but I can confirm that most of them only had vague memories of it. Now how can they fake finding out things if they knew it already? Because it was their subconscious that knew it. Komari subconsciously knew that her brother was dead but because of the circumstance, her active mind equated it as him being in some state of not-dead not-existing. Riki helped her realize her subconscious and make it her active thinking as to help her get over it
c: Funny thing: none of those items are actually explicitly said in the VN. You only get to understand them once you put two and two together 
As for what else happened, well, just Little Busters Little Buster-ing (without the five girls). Probably the only girl that would’ve interacted with them on a regular basis would have been Haru-chin as she is shown to be on good terms with them from the intro (that stint with Masato being her first encounter in the game and anime, for example)
