OMG! That is us, in a nutshell. The elementary PTO felt they had all the money, more classes, etc. They did not weant to join forces at all. The first year, since I wa now a middle school parent, I was the presdient and we did quite well, despite only having 3 classes to their 10. Our parent involvement was high as were our funds. This yer, they have bent over backward to join forces with us because most of us have been here a while and we know what works.
First, it all depends on the officers and how they feel. If one feels it should be split because they think they have/can make, more funds, let them! I have talked with the president of the middle parent group at our sister school, and splitting is really the best way.
Second, the funds need to be distributed fairly. This means something differrent to everyone. For us, it meant taking the number of students that we have in the middle school (60 to their 180) and using that as the factor for the funds. The total funds available at the end of the school year times the percentage of students that the middle school had and that was the check they wrote us as our starting funds. (25%)
Lastly, check the egos at the door. AS my recent post (One building, Two schools, Two PTOS's) shows, it is that some people feel VERY territorial about their PTO and do not want to share. Not everyone follows the rules of the playground, so just let go and enjoy your successes.
Good Luck!
