There are several different summary-style books about Robert's Rules that put the 100's of pages in easier to read format. My two personal favorites are little $5 books by D. Patnode and D. Zimmerman (you can get them at any bookstore). They're far less intimidating than the whole RRO. I refer to both books when I am researching an RRO issue so I can see how two different editors interpret the rule. It was a very worthwhile $10 investment.
Bylaws are a must, I agree. There is a sample set here on this website at the Bonus Tools page. There's also a one-page grossly simplified RRO cheat sheet for PTOs.
www.ptotoday.com/bonusTools.html
If your major issue is with handling funds, there are several key financial controls any group that handles money should implement.
1. Every financial transaction should be backed up by a paper trail - standard form, all information completed, receipts, invoices, etc.
2. Every check (and its associated control form) should be signed by 2 authorized officers. Blank checks should never be pre-signed for "convenience".
3. The bank account must be reconciled every month. Also, the bank should mail the monthly statement to someone other than the treasurer who gives the statement a quick review, and then passes it to the treasurer for reconciliation.
4. Deposits must be counted by 2 separate parties and deposited quickly.
5. Every month, whether or not you have a formal PTO meeting, your treasurer must report the financial picture of the PTO. At minimum, this would be a listing of the beginning balance, followed by all the credits (deposits), followed by all the debits (withdrawals and checks written), with the ending balance at the bottom. If you create a budget, the report should show performance against each budget category.
6. Your bylaws or at least some sort of written operating procedures until you adopt bylaws, should stipulate how spending decisions are made. Our Exec Board, by majority vote, can authorize up to $100 in unbudgeted expenses without the vote at a PTO meeting. Our principal has no access to our money except through us.
7. At the end of your fiscal year (probably in August or july), your financial files "books" need to be reviewed by an independent person or committee ("audit"). No one with check signing privileges should be on this review committee. You do not need to pay for this service. A parent volunteer(s) can do it.
If your NEW group implements financial controls now, they will become just the way things are done from the start. No biggy. No insinuation that anyone is doing anything wrong. Just sound business practice. Your group is still getting organized. This is the time to set up the highest quality organization possible. Frame your suggestions that way and maybe they'll understand you're not picking on anyone or coming off like a know it all.