Robyn,
From what I gather you're upset and frustrated because the current Parents Group officers are not following the by-laws or what's been done successfully in the past and are leaving you out of the decision making process. They're spending money on things that should have been approved by the general group.
(it would really, really help if you would double space once in a while to make the posts easier to read.)
I'm not sure what advice you are looking for but I'll try to help. First off, you need to take one issue at a time. As I'm sure you've read time and again by-laws and budgets are key to a well run parents group. I would suggest that you try to get both of those enforced or started if you don't have them. I would also try to enlist the support of other parents. It sounds like you have a hard time speaking your mind. I understand, but unless they can read your mind they will not know how you feel.
So, starting off with one item: the book fair. where you said that the Treasurer would be attending it and all other events. Makes sense to me but are you saying that she would be there by herself? I can't imagine why she would want or be able to do that. Our by-laws state that all money must be counted by two people. I can't say that we always follow this rule but there is always a paper trail at the book fair because volunteers write down the purchases and that matches up with the inventory. If you think she shouldn't be there alone, then speak up but just do it in a non-accusatory way.
Another issue, executive board meetings. I would find the time to attend these and SPEAK UP.
What I would do if I were in your shoes: Figure out what you really want to continue to do at your school and back off from everything else. If you are a single mom raising 5 kids and in college, I would make college my priority and back away from most school things as much as possible. Other people will step to the plate if you don't do it and if they don't the world won't end. It's hard to watch other people screw up what you've helped build but unless you can voice your opinion and get some more people to see your point of view you are going to be continually frustrated. I wish you the best.