Hmm.. Let's see, here...
Starting with Chapter 1
Nobody likes feeling left out of roleplays. ._. That's a plain and simple fact.
However, when that happens in roleplay (be it in-game or on a forum), I think it's best to continue moving along, and assume (for a while, anyway) that it's just a fluke, and the others might just be caught up in their posts. Try making your own posts very concise and clear, have your character very distinctly interact or start some interaction with their characters, that way it allows you a window into the roleplay. However, if it does keep up, then take it up with the roleplay leader, and if that still doesn't help, then (and only then) would I let them know that I'd be taking my leave.
So, give them the benefit of a doubt, but... If they're going to ignore you deliberately for extended periods of time, it probably isn't worth your time, anyway.
Chaptah 2
Again, I'm assuming this is forum-based roleplay?
The problem with being on the internet is that not everybody can be on all at once, all of the time. As you said, everybody's gotta get some sleep in, after all!
And so, if the RP is intense and very centered around your character and a few others, then it would be simple courtesy for the others to wait until tomorrow, as in any RP, for you to return.
Conversely, though, the RP isn't always based around a single person. There are often several storylines going on at once, and so if the RP had to stop every time someone had to go offline, I don't know if it would ever get anywhere in the story. o:> Then it would be difficult for anyone to stay interested in it at all. :L
That said, it just takes a lot of cooperation... As a fairly seasoned RPer, myself, I know I've had to go offline, only to come back to the RP, and it's wayyy ahead of where I left off, but that's usually when you've just gotta make up a story for what your character was doing previously, and do what you can to jump back in. Hang in there, Thrilleh. <3
Chaptah 3
Personally, I've always enjoyed seeing someone who's willing to jump up and lend a paw to help out the RP leaders, but generally (unless otherwise specified) it's best not to do things like updating the thread by oneself or accepting new members without consent of the roleplay leader...
While I'm not too familiar with the differences between forum vs. in-game roleplay etiquette, I do know that that right is reserved for the RP leader and the ones that leader has given authority to do so in their absence.
Again, this could differ from roleplay to roleplay, depending on the individuals. If you do think these kids are doing something they ought not to, though, why not point it out to the actual roleplay leader? It couldn't hurt, after all.
I'm sorry you've had a rough time, though... These are just my thoughts on all of that, though. Take it easy, Thrilleh, and just remember to have fun. <3
(By the way. Your new siggy is ADORABLE! 8D)