Is it permissible to divide the money collected for a poor family between them and another family that is poorer?

Your action regarding financial aid depends on the donor's intention. If your colleagues intended their money to be given to a specific family, then it is not permissible to disburse it to others without their permission. However, if their intention was to donate to the poor in general, then it is permissible to disburse it to the two poor families. The rule is that whoever receives funds for a specific purpose may not spend them on anything else except after seeking permission from their owners.