Create Function for Getting Core Data Objects with Proper Relationships

I am looking for an Objective C developer experienced in arrays, Core Data, and loops who would be able to help me create the loop function I'm looking for. I'd rather not write about my entire project here but essentially I have this: -Many objects in Core Data system with a one-to-many relationship. -Depending on the input provided, I would like to get the objects from the core data with the corresponding name in the correct order (which I already can do) BUT only start from a certain 'many' until another 'many. They already have a 'position' attribute which is a NSNumber and keeps things in order. So an example: my father is the 'one' and the 'many' are children. I want to get the right father (since there could be two with the same name) and then from all of his children (example, 20 children) start and end at the correct children given in the parameters of the function. These children are already in order with a position attribute in Core data (NSNumber) so that makes things easier. As for the many fathers, it is possible two or even three have the same name but only one of them will have the right children and with the 'start' children parameter before the 'end' child parameter. So you'd have to code that login in as well (to pick the right father where endChild is after startChild in the data). My core data relationships are already set up perfectly and I can import all the data, I use some NSManagedObject classes as well for Father and Child to access their data, the problem I am having is the loop/method setup to all this working how I want it to. Let me know if you need more info. I look forward to your responses. Mike