According Lifestream Black, Sephiroth had to shed his memories of what he looked like in order to stay coherent. The SHM were supposed to regain these memories for him. So it could be that they were just waiting around, not sure what to do other than knowing they are driven by Sephiroth's will to regain certain memories and then merge with Jenova. Because I mean, he couldn't manifest again if he didn't even know what he looked like, unless he wanted to make something up and look different but I'm guessing that was not the case.
Of course, the fact that their clothes were still manifesting could indicate that they had just manifested in the living world. I sometimes wonder if they started out as babies and then grew.
lol
As for the bikes I think it mentions in an Ultimania somewhere that they were stolen?